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P2122 Throttle/Pedal Position Sensor/Switch "D" Circuit Low Input
The P2122 Throttle/Pedal Position Sensor/Switch "D" Circuit Low Input diagnostic trouble code indicates that the Engine Control Module (ECM/PCM) has detected a voltage signal from the throttle or accelerator pedal position D circuit that is lower than the expected range.
In simple terms, the vehicle's computer is receiving too little voltage from the D throttle/pedal position circuit.
Modern vehicles commonly use electronic throttle control (ETC) systems instead of a traditional mechanical accelerator cable. These systems use multiple throttle and accelerator pedal position signals to monitor accelerator-pedal movement and throttle position.
The ECM continuously monitors these signals and compares them with predefined operating ranges. If the D circuit voltage falls below the expected threshold, the ECM can store P2122, illuminate the Check Engine Light, and potentially activate a reduced-power or fail-safe mode.
Common symptoms include:
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Check Engine Light
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Poor throttle response
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Accelerator hesitation
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Reduced engine power
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Limited acceleration
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Limp mode
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Engine surging
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Rough idle
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Engine stalling
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Cruise-control deactivation
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Electronic throttle warning messages
The exact component associated with the D circuit is manufacturer-specific. It may be part of the accelerator pedal position sensor system, electronic throttle body, or another throttle/pedal position circuit.
What Does P2122 Mean?
P2122 means that the ECM/PCM has detected a low-input voltage condition in the throttle/pedal position sensor or switch D circuit.
The important term is "Low Input."
The ECM expects the D circuit signal to remain within a specific voltage range. When the voltage falls below the manufacturer's calibrated threshold, P2122 may be stored.
A low signal can be caused by:
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Signal wire shorted to ground
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Open or high-resistance reference circuit
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Faulty position sensor
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Faulty accelerator pedal assembly
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Faulty electronic throttle body
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Poor sensor power supply
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Poor sensor ground
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Damaged wiring
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Corroded connector
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Loose electrical terminal
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Internal sensor failure
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ECM/PCM fault
A P2122 code does not automatically mean that the accelerator pedal or throttle body must be replaced.
What Is the Throttle/Pedal Position Sensor?
Modern electronic throttle systems use position sensors to determine how far the accelerator pedal is being pressed and how far the throttle plate is open.
A typical electronic throttle system works as follows:
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The driver presses the accelerator pedal.
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Accelerator pedal position sensors detect pedal movement.
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The sensors generate electrical signals.
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The ECM/PCM receives these signals.
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The ECM calculates the driver's requested torque.
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The ECM commands the electronic throttle actuator.
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The throttle plate moves.
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Throttle position sensors report actual throttle position.
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The ECM compares the available signals for plausibility and safety.
Multiple position signals provide redundancy.
If one of these signals becomes abnormally low, the ECM may recognize the problem and activate a protective strategy.
What Does "D Circuit" Mean?
The D circuit refers to a specific throttle or accelerator pedal position signal identified by the manufacturer.
It does not necessarily mean there is a separate physical component called "Sensor D."
Depending on the vehicle, the D circuit may be associated with:
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Accelerator pedal position sensor
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Throttle position sensor
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Electronic throttle body
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One of several redundant sensor signals
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Accelerator pedal assembly
The exact location and function of the D circuit must be confirmed using the vehicle-specific:
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Wiring diagram
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Connector pinout
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Sensor specifications
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Service information
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Manufacturer diagnostic procedure
The D circuit on one vehicle can be different from the D circuit on another vehicle.
What Does "Low Input" Mean?
The ECM monitors the electrical voltage generated by the D circuit.
Under normal operation, the signal should remain within a defined range as the accelerator pedal or throttle moves.
A simplified example:
Normal operation
The D signal changes smoothly within its specified operating range.
Low-input condition
The D signal falls below the minimum voltage expected by the ECM.
This may happen because:
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The signal wire is shorted to ground.
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The sensor has an internal fault.
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The reference voltage is missing.
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The sensor ground is faulty.
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A connector terminal is damaged.
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The wiring has excessive resistance.
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The sensor is disconnected.
The exact voltage threshold is vehicle-specific and should always be confirmed using manufacturer service information.
Symptoms of P2122
Symptoms depend on the vehicle and severity of the low-input condition.
Check Engine Light
The Check Engine Light is commonly illuminated.
Poor Throttle Response
The accelerator may respond slowly or incorrectly.
Hesitation
The engine may hesitate when the accelerator is pressed.
Reduced Engine Power
The ECM may intentionally limit engine output.
Limited Acceleration
The vehicle may have difficulty accelerating normally.
Limp Mode
The ECM may enter a fail-safe operating strategy.
Engine Surging
Incorrect throttle-position information can produce abnormal engine response.
Rough Idle
Throttle-control problems can affect idle quality.
Engine Stalling
A severe loss of throttle-position information may contribute to stalling.
Cruise Control Disabled
Cruise control may be disabled because reliable throttle information is required.
Warning Messages
Depending on the vehicle, the dashboard may display messages such as:
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Reduced Engine Power
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Service Throttle System
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Electronic Throttle Control Fault
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Engine Fault
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Drive System Fault
Common Causes of P2122
Signal Wire Shorted to Ground
One of the most important causes of a low-input code is an unwanted connection between the D signal wire and ground.
Possible causes include:
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Chafed wiring
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Pinched harness
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Melted insulation
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Damaged connector
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Incorrect previous repair
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Harness contacting the engine or chassis
Faulty Throttle/Pedal Position Sensor
The position sensor itself may have an internal electrical failure.
Possible problems include:
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Internal short
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Incorrect output
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Damaged sensing element
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Sensor wear
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Internal contamination
Faulty Accelerator Pedal Position Sensor
If the D circuit belongs to the accelerator pedal assembly, the internal pedal-position sensor may be defective.
Possible failures include:
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Internal short circuit
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Low output voltage
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Sensor-element damage
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Internal electrical wear
Faulty Electronic Throttle Body
If the D circuit belongs to the electronic throttle body, an internal throttle-position sensor or electronic circuit may produce an excessively low signal.
Missing or Low Reference Voltage
Throttle and pedal position sensors commonly use a regulated reference voltage.
If the reference voltage is missing or too low, the sensor signal can also become abnormally low.
Possible causes include:
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Open reference wire
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Shorted reference circuit
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ECM reference-voltage problem
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Another sensor affecting a shared reference circuit
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Wiring damage
Poor Sensor Power Supply
Depending on the vehicle design, the position sensor may require a dedicated supply voltage.
A poor power supply can cause a low sensor output.
Possible causes include:
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Open power wire
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Blown fuse
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Poor connector contact
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Damaged wiring
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Power-supply circuit fault
Poor Sensor Ground
A sensor ground problem can affect the sensor's ability to produce a correct signal.
Possible causes include:
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Loose ground
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Corroded ground connection
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Broken ground wire
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High resistance
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Poor connector contact
Although a ground problem often produces unusual sensor readings rather than simply "low input," it should still be checked according to the manufacturer's diagnostic procedure.
Damaged Wiring
Inspect wiring for:
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Chafing
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Broken conductors
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Pinched wires
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Heat damage
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Vibration damage
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Melted insulation
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Previous repair problems
Corroded Electrical Connector
Corrosion can increase resistance or interrupt sensor circuits.
Look for:
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Green corrosion
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Oxidation
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White deposits
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Moisture
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Damaged terminals
Loose or Damaged Terminal
A loose or backed-out terminal can interrupt the sensor signal.
Possible problems include:
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Poor terminal tension
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Bent terminal
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Backed-out pin
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Damaged connector lock
Water Intrusion
Water entering a connector can cause:
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Corrosion
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Electrical shorts
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Increased resistance
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Intermittent sensor signals
Throttle Plate Contamination
Carbon deposits can restrict throttle movement.
This can contribute to throttle-position problems, although a dirty throttle body alone does not necessarily explain an electrical low-input circuit code.
Mechanical Throttle Binding
A sticking throttle plate can cause a mismatch between commanded and actual position.
Possible causes include:
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Carbon buildup
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Foreign material
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Damaged throttle shaft
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Mechanical wear
Low Battery or Charging Voltage
Unstable vehicle voltage can affect electronic throttle operation.
Possible causes include:
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Weak battery
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Loose battery terminal
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Alternator problems
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Poor engine ground
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Poor chassis ground
Throttle or Pedal Calibration Problem
Some vehicles require a relearn or calibration procedure after:
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Throttle-body replacement
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Accelerator-pedal replacement
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Battery disconnection
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ECM replacement
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Software update
Failure to complete a required procedure can result in related throttle-control codes.
Aftermarket Modifications
Potential causes include:
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Throttle-response controllers
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Pedal tuning devices
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Modified wiring
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ECU tuning
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Engine swaps
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Non-standard throttle components
Faulty ECM/PCM
An ECM/PCM fault is possible but generally less common than:
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Sensor problems
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Wiring faults
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Connector faults
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Reference-voltage problems
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Ground problems
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Throttle-body problems
The control module should generally be considered only after the external circuits and components have been properly tested.
Vehicles Commonly Affected by P2122
P2122 can occur on many OBD-II vehicles equipped with electronic throttle-control systems.
Examples may include:
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Ford F-150
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Ford Explorer
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Ford Mustang
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Ford Focus
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Ford Ranger
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Chevrolet Silverado
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Chevrolet Tahoe
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Chevrolet Malibu
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Chevrolet Camaro
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GMC Sierra
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GMC Yukon
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Cadillac Escalade
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Dodge Charger
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Dodge Challenger
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Ram 1500
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Jeep Grand Cherokee
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Jeep Wrangler
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Chrysler Pacifica
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Toyota Camry
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Toyota Tundra
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Toyota Tacoma
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Honda Accord
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Honda Civic
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Honda CR-V
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Nissan Altima
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Nissan Pathfinder
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Nissan Titan
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BMW 3 Series
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BMW 5 Series
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Mercedes-Benz C-Class
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Mercedes-Benz E-Class
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Volkswagen Golf
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Volkswagen Passat
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Audi A4
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Audi A6
This list is not exhaustive.
P2122 can occur on any compatible vehicle when the ECM detects that the relevant throttle/pedal position D circuit signal is below its expected range.
Important: The exact component, connector, voltage threshold, and circuit location vary by manufacturer.
How Is P2122 Diagnosed?
P2122 should be diagnosed using the vehicle manufacturer's wiring diagrams, specifications, scan-tool data, and diagnostic procedures.
The objective is to determine whether the low signal is caused by:
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Sensor failure
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Accelerator pedal assembly
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Electronic throttle body
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Signal wire shorted to ground
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Missing reference voltage
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Low sensor power supply
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Ground problem
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Connector fault
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Wiring damage
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Mechanical throttle problem
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Calibration issue
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ECM/PCM fault
Check for Additional Trouble Codes
Perform a complete diagnostic scan.
Look for:
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P2121
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P2122
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P2123
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P2124
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P2125
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P2126
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P2127
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P2128
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P2129
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P2130–P2140
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Throttle actuator codes
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Accelerator pedal position codes
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5-volt reference codes
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Sensor circuit codes
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Battery-voltage codes
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Communication codes
Related codes can reveal whether the problem is isolated to the D circuit or affects multiple throttle/pedal signals.
Check Freeze-Frame Data
Review the freeze-frame information captured when P2122 was stored.
Useful parameters may include:
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Engine RPM
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Vehicle speed
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Engine load
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Battery voltage
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Accelerator pedal position
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Throttle position
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Coolant temperature
This can help determine whether the problem occurred during:
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Acceleration
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Deceleration
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Cruising
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Idle
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Engine startup
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A particular temperature condition
Identify the D Circuit
Use the vehicle-specific wiring diagram to identify:
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D signal wire
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Reference-voltage circuit
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Sensor power supply
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Sensor ground
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ECM/PCM terminal
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Related redundant sensor
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Connector pin numbers
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Expected voltage range
Do not assume that the D circuit uses the same connector pin or voltage specification on another vehicle.
Monitor Live Data
Use a capable scan tool to monitor:
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D circuit position
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Accelerator pedal position
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Throttle position
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Other redundant position signals
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Commanded throttle position
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Actual throttle position
Slowly operate the accelerator pedal through its full range.
Look for:
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D signal stuck low
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Signal below the expected range
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Abnormal signal changes
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Signal dropouts
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Mismatch with redundant signals
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Unexpectedly low position values
Measure the D Signal Voltage
Use a multimeter according to the manufacturer's diagnostic procedure.
Measure:
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D signal voltage
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Reference voltage
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Sensor power supply, if applicable
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Sensor ground
Compare the results with the manufacturer's specifications.
Do not apply battery voltage or ground directly to a sensor circuit unless the manufacturer's diagnostic procedure specifically instructs you to do so.
Check the Reference Voltage
Many throttle and pedal systems use a regulated reference voltage, commonly around 5 volts, but the exact specification must be confirmed for the specific vehicle.
If the reference voltage is missing or too low, investigate the reference circuit before replacing the sensor.
Check Sensor Power Supply
If the system uses a dedicated sensor power supply, verify that it is present and within specification.
Check for:
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Open circuits
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Blown fuses
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Poor terminal contact
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Voltage drop
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Damaged wiring
Check Sensor Ground
Verify that the sensor ground is within specification.
Check for:
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Excessive resistance
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Voltage drop
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Corrosion
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Loose connections
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Damaged ground wiring
Check for a Short to Ground
Because P2122 specifically indicates a low-input condition, inspect the D signal wire for an unwanted connection to:
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Chassis ground
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Engine ground
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Another grounded circuit
A signal wire shorted to ground can pull the sensor voltage down.
Check for an Open or High-Resistance Circuit
Inspect the D circuit for:
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Broken wires
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Damaged terminals
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Poor splices
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Corrosion
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High resistance
Perform continuity and resistance testing according to the manufacturer's procedure.
Inspect Electrical Connectors
Check for:
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Corrosion
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Water intrusion
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Bent pins
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Loose terminals
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Backed-out pins
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Damaged connector locks
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Melted insulation
Perform a Wiggle Test
While monitoring live sensor data, carefully move the relevant wiring harness and connectors.
If the D signal suddenly changes, inspect the wiring and connector more closely.
This can help identify:
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Broken internal wires
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Loose terminals
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Poor connector contact
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Harness damage
Inspect the Accelerator Pedal
If the D circuit belongs to the accelerator pedal assembly, inspect:
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Pedal movement
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Position sensor
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Connector
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Wiring
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Terminals
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Physical damage
The pedal should move smoothly without binding.
Inspect the Electronic Throttle Body
If the D circuit belongs to the throttle body, inspect:
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Throttle plate
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Position sensors
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Actuator
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Internal wiring
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Connector
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Electronic components
Compare Redundant Sensor Signals
Compare the D signal with the other relevant throttle or accelerator pedal position signals.
If the D signal is abnormally low while the other signals remain normal, investigate the D circuit and its associated sensor.
Check Commanded vs. Actual Throttle Position
Compare commanded throttle position with actual throttle position.
An unexpected difference may indicate:
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Position-sensor failure
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Electronic throttle-body fault
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Mechanical binding
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Wiring problems
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Actuator problems
Check Battery and Charging Voltage
Verify:
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Battery voltage
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Battery terminals
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Alternator output
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Charging voltage
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Engine grounds
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Chassis grounds
Use an Oscilloscope When Necessary
An oscilloscope can help identify:
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Voltage dropouts
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Signal glitches
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Electrical noise
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Intermittent low-voltage events
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Irregular sensor waveforms
This can be useful when the fault is difficult to reproduce with a multimeter.
Check for Technical Service Bulletins
Check manufacturer service information for known:
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Accelerator pedal faults
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Throttle-body problems
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Wiring issues
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Connector problems
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Software updates
How to Fix P2122
The correct repair depends on the confirmed cause.
Repair a Signal Wire Shorted to Ground
Repair damaged wiring and restore the correct signal-circuit routing.
Replace a Faulty Position Sensor
If testing confirms that the sensor itself is producing an abnormally low signal, replace the applicable sensor.
Replace the Accelerator Pedal Assembly
If the D circuit is integrated into the accelerator pedal and the internal sensor has failed, replace the pedal assembly when required.
Replace the Electronic Throttle Body
If an internal throttle-position sensor, actuator, or electronic circuit is defective, replace the throttle body or applicable assembly.
Repair Reference-Voltage Problems
Repair the reference circuit if testing confirms that the voltage is missing or below specification.
Repair Sensor Power-Supply Problems
Repair an open power circuit, blown fuse, damaged wire, or poor electrical connection when confirmed by testing.
Repair Sensor Ground Problems
Repair loose, corroded, damaged, or high-resistance ground connections.
Repair Damaged Wiring
Repair or replace wiring affected by:
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Heat
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Chafing
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Vibration
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Pinching
-
Corrosion
-
Previous repairs
Repair or Replace Electrical Connectors
Replace damaged terminals or connector housings and restore correct terminal tension.
Repair Water Intrusion
Replace damaged connector seals and correct the source of moisture.
Repair Mechanical Throttle Problems
Repair the throttle mechanism if the throttle plate or shaft is physically binding.
Clean the Throttle Body
If carbon buildup is confirmed to be restricting throttle movement, clean the throttle body according to the manufacturer's procedure.
Perform Required Relearn Procedures
Some vehicles may require:
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Throttle body relearn
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Accelerator pedal calibration
-
Idle relearn
-
Electronic throttle adaptation
Follow the manufacturer-specific procedure.
Correct Aftermarket Modifications
Remove or correct aftermarket throttle-control devices if they are responsible for the abnormal signal.
Update ECM/PCM Software
If manufacturer service information identifies a software-related issue, perform the appropriate ECM/PCM update.
Replace the ECM/PCM
The ECM/PCM should only be considered after the sensor, wiring, connectors, reference voltage, power supply, grounds, and throttle/pedal assembly have been properly tested.
What Happens If P2122 Is Ignored?
P2122 should not be ignored because the fault involves an accelerator or throttle position circuit.
Possible consequences include:
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Reduced engine power
-
Poor acceleration
-
Hesitation
-
Limp mode
-
Engine stalling
-
Unpredictable throttle response
-
Cruise-control deactivation
-
Poor fuel economy
-
Additional throttle-control codes
-
Increased emissions
The ECM may intentionally limit throttle operation when it cannot trust the position signal.
Can You Drive With P2122?
Driving with P2122 should be approached cautiously.
A vehicle with this code may enter reduced-power mode or respond differently to accelerator input.
A short trip may be possible if:
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Accelerator response is predictable.
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The engine runs normally.
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There is no significant power loss.
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The vehicle is not stalling.
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No serious warning messages are displayed.
Avoid continued driving if you experience:
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Sudden power loss
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Unpredictable accelerator response
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Severe hesitation
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Repeated stalling
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Reduced-power mode
-
Multiple electronic throttle warnings
If accelerator response becomes unpredictable, have the vehicle inspected promptly.
Is P2122 a Serious Code?
P2122 is generally considered a moderate to potentially high-severity diagnostic trouble code.
The code affects a throttle or accelerator position circuit, which is important to engine control and vehicle response.
Depending on the vehicle, the ECM may:
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Enter fail-safe mode
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Limit engine power
-
Disable cruise control
-
Restrict throttle operation
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Trigger a reduced-power warning
If there is sudden loss of acceleration, engine stalling, or unpredictable accelerator response, the fault should be treated as high priority.
How to Prevent P2122
Recommended practices include:
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Protect throttle and accelerator-pedal wiring from heat.
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Prevent wiring from rubbing against metal.
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Keep electrical connectors clean and dry.
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Check connector seals for water intrusion.
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Maintain battery terminals.
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Maintain engine and chassis grounds.
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Repair damaged wiring promptly.
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Secure wiring away from moving engine components.
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Avoid poorly installed throttle-control modifications.
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Use correct replacement components.
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Perform required throttle or pedal relearn procedures.
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Inspect wiring after major engine repairs.
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Address Check Engine Light warnings promptly.
P2122 vs. Related Codes
| Code | General Description |
|---|---|
| P2121 | Throttle/Pedal Position Sensor/Switch "D" Circuit Range/Performance |
| P2122 | Throttle/Pedal Position Sensor/Switch "D" Circuit Low Input |
| P2123 | Throttle/Pedal Position Sensor/Switch "D" Circuit High Input |
| P2124 | Throttle/Pedal Position Sensor/Switch "D" Circuit Intermittent |
| P2125 | Throttle/Pedal Position Sensor/Switch "E" Circuit Malfunction |
| P2126 | Throttle/Pedal Position Sensor/Switch "E" Circuit Range/Performance |
| P2127 | Throttle/Pedal Position Sensor/Switch "E" Circuit Low Input |
| P2128 | Throttle/Pedal Position Sensor/Switch "E" Circuit High Input |
| P2129 | Throttle/Pedal Position Sensor/Switch "E" Circuit Intermittent |
| P2130 | Throttle/Pedal Position Sensor/Switch "F" Circuit Malfunction |
| P2131 | Throttle/Pedal Position Sensor/Switch "F" Circuit Range/Performance |
| P2132 | Throttle/Pedal Position Sensor/Switch "F" Circuit Low Input |
| P2133 | Throttle/Pedal Position Sensor/Switch "F" Circuit High Input |
| P2134 | Throttle/Pedal Position Sensor/Switch "F" Circuit Intermittent |
| P2135 | Throttle Position Sensor A/B Voltage Correlation |
| P2136 | Throttle/Pedal Position Sensor/Switch A/C Voltage Correlation |
| P2137 | Throttle/Pedal Position Sensor/Switch B/C Voltage Correlation |
| P2138 | Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation |
| P2139 | Throttle/Pedal Position Sensor/Switch D/F Voltage Correlation |
| P2140 | Throttle/Pedal Position Sensor/Switch E/F Voltage Correlation |
The D-circuit codes can be summarized as:
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P2121 = D circuit range/performance
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P2122 = D circuit low input
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P2123 = D circuit high input
-
P2124 = D circuit intermittent
The P2125–P2129 codes relate to the corresponding E circuit, while P2130–P2134 relate to the F circuit.
Final Thoughts
The P2122 Throttle/Pedal Position Sensor/Switch "D" Circuit Low Input diagnostic trouble code indicates that the ECM/PCM has detected a throttle or accelerator pedal position D-circuit signal that is below the expected electrical range.
Common causes include:
-
Signal wire shorted to ground
-
Missing or low reference voltage
-
Poor sensor power supply
-
Faulty throttle position sensor
-
Faulty accelerator pedal position sensor
-
Faulty electronic throttle body
-
Poor sensor ground
-
Damaged wiring
-
Corroded connectors
-
Loose or backed-out terminals
-
Water intrusion
-
Mechanical throttle problems
-
Low or unstable system voltage
-
Calibration problems
-
Aftermarket modifications
-
ECM/PCM faults
The most important point is that P2122 does not automatically mean that the throttle body or accelerator pedal must be replaced.
Diagnosis should begin by identifying the D circuit and checking the signal voltage, reference voltage, sensor power supply, sensor ground, wiring, connectors, and possible shorts to ground. Live-data comparison with redundant throttle or pedal-position signals can help determine whether the fault is isolated to the D circuit.
If the signal remains low even when the pedal or throttle position changes, the sensor and its power, ground, and signal circuits should be tested before replacing components.
If the vehicle experiences reduced engine power, sudden acceleration problems, engine stalling, or unpredictable accelerator response, the fault should be diagnosed promptly.
Correctly identifying the source of the low-input condition can prevent unnecessary parts replacement and help restore safe and reliable electronic throttle operation.
