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P2123 Throttle/Pedal Position Sensor/Switch "D" Circuit High Input
The P2123 Throttle/Pedal Position Sensor/Switch "D" Circuit High 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 higher than the expected range.
In simple terms, the vehicle's computer is receiving too much 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 driver input and throttle movement.
The ECM continuously compares these signals with expected voltage ranges. If the D circuit voltage becomes too high, the ECM can store P2123, illuminate the Check Engine Light, and in some vehicles 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 varies by manufacturer. It may be part of the accelerator pedal position sensor system, electronic throttle body, or another throttle/pedal position circuit.
What Does P2123 Mean?
P2123 means that the ECM/PCM has detected a high-input voltage condition in the throttle/pedal position sensor or switch D circuit.
The important term is "High Input."
The ECM expects the D circuit to operate within a specified electrical range. When the signal voltage rises above the manufacturer's calibrated threshold, P2123 may be stored.
A high signal can be caused by:
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Signal wire shorted to battery voltage
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Incorrect reference voltage
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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 ground
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Damaged wiring
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Incorrect wiring repair
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Connector problems
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Internal sensor failure
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ECM/PCM fault
A P2123 code does not automatically mean that the throttle body or accelerator pedal needs to be replaced.
What Is the Throttle/Pedal Position Sensor?
Modern electronic throttle systems use electrical sensors to determine accelerator-pedal and throttle position.
A typical electronic throttle system operates 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 produce electrical signals.
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The ECM/PCM receives the signals.
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The ECM calculates the requested engine 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 the actual position.
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The ECM compares the available signals for plausibility and safety.
Multiple position signals provide redundancy.
If one circuit reports an implausibly high voltage, the ECM can recognize the discrepancy and activate a protective strategy.
What Does "D Circuit" Mean?
The D circuit is a specific throttle or 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, D may refer to:
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Accelerator pedal position sensor circuit
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Throttle position sensor circuit
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Electronic throttle body signal
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One of several redundant position signals
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Accelerator pedal assembly circuit
The exact meaning of D is manufacturer-specific.
The correct circuit must be identified using the vehicle's:
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Wiring diagram
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Connector pinout
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Technical specifications
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Service information
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Manufacturer diagnostic procedure
The D circuit on one vehicle may be completely different from the D circuit on another vehicle.
What Does "High Input" Mean?
The ECM monitors the voltage produced by the D circuit.
Under normal conditions, the signal should remain within a defined operating range.
A simplified example might look like this:
Normal sensor operation
The sensor signal changes through its expected voltage range as the pedal or throttle moves.
High-input condition
The D signal becomes higher than the maximum voltage the ECM expects.
This can happen if:
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The signal wire contacts battery voltage.
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The sensor internally fails.
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The reference circuit is abnormal.
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The sensor ground becomes faulty.
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A connector terminal is damaged.
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Wiring has been incorrectly repaired.
The exact voltage threshold is vehicle-specific and should not be assumed.
Symptoms of P2123
Symptoms depend on the vehicle and severity of the high-input condition.
Check Engine Light
The Check Engine Light is commonly illuminated.
Poor Throttle Response
The accelerator may respond incorrectly or slowly.
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 not accelerate normally.
Limp Mode
The ECM may enter a fail-safe operating mode.
Engine Surging
Incorrect throttle-position information can cause abnormal engine response.
Rough Idle
Throttle-control problems may affect idle stability.
Engine Stalling
A severe throttle-control fault can contribute to engine stalling.
Cruise Control Disabled
Cruise control may be disabled when throttle information is unreliable.
Warning Messages
Depending on the vehicle, the dashboard may display:
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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 P2123
Signal Wire Shorted to Power
One of the most important causes of a high-input code is an unwanted connection between the D signal wire and a power source.
Possible causes include:
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Chafed wiring
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Melted insulation
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Pinched harness
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Incorrect previous repair
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Damaged connector
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Harness contacting another power wire
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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Sensor-element failure
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Damaged sensing track
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Internal contamination
Faulty Accelerator Pedal Position Sensor
If the D circuit belongs to the accelerator pedal assembly, the pedal-position sensor may be defective.
Possible failures include:
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Internal short circuit
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Incorrect voltage output
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Sensor-element damage
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Electrical wear
Faulty Electronic Throttle Body
If the D circuit is part of the throttle body, an internal throttle-position sensor or electronic circuit may produce an excessively high signal.
Incorrect Reference Voltage
Throttle and pedal position sensors commonly use a regulated reference voltage.
If the reference voltage becomes higher than specified, the sensor output may also become abnormal.
Possible causes include:
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Reference-wire short to power
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ECM reference-voltage problem
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Another sensor affecting a shared reference circuit
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Wiring fault
Poor Sensor Ground
A sensor ground problem can cause the output voltage to behave abnormally.
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
Damaged Wiring
Inspect wiring for:
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Chafing
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Broken conductors
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Melted insulation
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Pinched wires
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Heat damage
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Vibration damage
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Incorrect previous repairs
Corroded Electrical Connector
Corrosion can interfere with sensor signals and reference circuits.
Inspect 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 terminal that is bent, loose, or improperly seated can cause abnormal sensor voltage.
Possible problems include:
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Poor terminal tension
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Backed-out pin
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Bent pin
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Damaged connector lock
Water Intrusion
Water inside an electrical connector can cause:
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Corrosion
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Unstable resistance
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Electrical shorts
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Abnormal sensor signals
Throttle Plate Contamination
Carbon deposits can restrict throttle movement.
This may contribute to throttle-position problems, although a dirty throttle body alone does not necessarily explain a high-input electrical circuit code.
Mechanical Throttle Binding
A sticking throttle plate can prevent the throttle from following the expected 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 Problems
Unstable system 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 specific calibration or relearn 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 perform a required procedure can cause related throttle-control faults.
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 a wiring, sensor, connector, reference-voltage, or ground problem.
The control module should normally be considered only after the external circuit has been thoroughly tested.
Vehicles Commonly Affected by P2123
P2123 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.
P2123 can occur on any compatible vehicle when the ECM detects that the relevant throttle/pedal position D circuit signal is above its expected range.
Important: The exact component, connector, voltage threshold, and circuit location vary by manufacturer.
How Is P2123 Diagnosed?
P2123 should be diagnosed using the vehicle manufacturer's wiring diagrams, specifications, scan-tool data, and diagnostic procedures.
The objective is to determine whether the high 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 power
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Reference-voltage problem
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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 show 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 P2123 was stored.
Useful information 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 fault 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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Startup
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A specific 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 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 the D circuit uses the same pin or voltage threshold 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.
Look for:
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D signal stuck high
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Signal above the expected range
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Abnormal signal changes
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Mismatch with redundant signals
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Unexpectedly high 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 ground
Compare the measurements with the manufacturer's specifications.
Do not apply battery voltage to a sensor signal 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 vehicle.
If the reference voltage is too high, investigate the reference circuit before replacing the sensor.
Check Sensor Ground
Verify that the sensor ground is correct.
Look 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
A ground problem can make a sensor output appear abnormal.
Check for a Short to Power
Because P2123 specifically indicates a high-input condition, inspect the D signal wire for unwanted contact with:
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Battery voltage
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Ignition voltage
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Another powered circuit
A short to power is especially important to rule out before replacing a sensor.
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 changes unexpectedly, inspect the harness 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, 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 and return correctly.
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 signals.
If one signal is abnormally high while the others remain within specification, investigate the corresponding D circuit.
Check Commanded vs. Actual Throttle Position
Compare commanded throttle position with actual throttle position.
An abnormal 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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Signal spikes
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Electrical noise
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Abnormal voltage patterns
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Intermittent high-voltage events
This can be useful when the signal problem is difficult to reproduce.
Check for Technical Service Bulletins
Check manufacturer service information for known:
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Accelerator pedal faults
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Throttle-body failures
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Wiring problems
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Connector issues
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Software updates
How to Fix P2123
The correct repair depends on the confirmed cause.
Repair a Signal Wire Shorted to Power
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 incorrect high 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 outside specification.
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
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Corrosion
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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
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Idle relearn
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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, grounds, and throttle/pedal assembly have been properly tested.
What Happens If P2123 Is Ignored?
P2123 should not be ignored because the fault involves an accelerator or throttle position circuit.
Possible consequences include:
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Reduced engine power
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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 P2123?
Driving with P2123 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
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Multiple electronic throttle warnings
If accelerator response becomes unpredictable, have the vehicle inspected promptly.
Is P2123 a Serious Code?
P2123 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
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Disable cruise control
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Restrict throttle operation
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Trigger a reduced-power warning
If there is sudden loss of acceleration, engine stalling, or unpredictable throttle response, the fault should be treated as high priority.
How to Prevent P2123
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.
P2123 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
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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 P2123 Throttle/Pedal Position Sensor/Switch "D" Circuit High Input diagnostic trouble code indicates that the ECM/PCM has detected a throttle or accelerator pedal position D-circuit signal that is higher than the expected electrical range.
Common causes include:
-
Signal wire shorted to power
-
Faulty throttle position sensor
-
Faulty accelerator pedal position sensor
-
Faulty electronic throttle body
-
Incorrect reference voltage
-
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 P2123 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 ground, wiring, connectors, and possible shorts to power. Live-data comparison with redundant throttle or pedal-position signals is also extremely useful.
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 high-input condition can prevent unnecessary parts replacement and help restore safe and reliable electronic throttle operation.
