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P2135 Throttle Position Sensor A/B Voltage Correlation
The P2135 Throttle Position Sensor A/B Voltage Correlation diagnostic trouble code indicates that the Engine Control Module (ECM/PCM) has detected that the signals from Throttle Position Sensor A and Throttle Position Sensor B are not maintaining the expected voltage relationship.
In simple terms, the vehicle's computer is receiving two throttle-position signals that should correspond with each other, but they are not agreeing as expected.
Modern electronic throttle control systems commonly use multiple throttle position signals for redundancy and safety. The ECM continuously compares Sensor A and Sensor B. If the difference between the two signals becomes greater than the manufacturer's programmed limit, the ECM can store P2135.
Depending on the vehicle, P2135 may cause the Check Engine Light, reduced engine power, poor throttle response, hesitation, limp mode, poor acceleration, engine surging, rough running, or stalling.
The exact sensor configuration varies by vehicle. Sensor A and Sensor B are commonly integrated into the electronic throttle body, although the precise circuit arrangement and diagnostic specifications depend on the manufacturer.
What Does P2135 Mean?
P2135 means that the ECM/PCM has detected a voltage correlation problem between Throttle Position Sensor A and Throttle Position Sensor B.
The two sensors do not necessarily produce identical voltages.
Instead, they are designed to produce signals that have a predictable relationship as the throttle plate moves.
For example:
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Sensor A may increase as throttle opening increases.
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Sensor B may also change but use a different voltage range or signal pattern.
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The ECM compares both signals continuously.
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The difference between them must remain within a specified range.
If one signal changes incorrectly, becomes unstable, drops out, or does not follow the expected relationship, P2135 may be stored.
What Is a Throttle Position Sensor?
A Throttle Position Sensor (TPS) monitors the position of the throttle plate and provides position information to the ECM/PCM.
In an electronic throttle control system, the throttle body may contain:
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Throttle actuator motor
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Throttle Position Sensor A
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Throttle Position Sensor B
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Internal wiring
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Electronic control components
The ECM uses throttle position information to control engine operation.
It may use this information for:
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Fuel control
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Ignition control
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Engine torque management
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Transmission operation
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Idle control
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Cruise control
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Traction and stability systems
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Emissions control
Because throttle position is important to engine control, multiple signals may be used to verify that the reported position is correct.
Why Are Two Throttle Position Sensors Used?
Using two position signals provides redundancy.
The ECM can compare the signals instead of relying on only one sensor.
A typical electronic throttle system works like this:
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The accelerator pedal is pressed.
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The ECM interprets the accelerator pedal position.
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The ECM commands the throttle actuator.
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The throttle motor moves the throttle plate.
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Sensor A reports throttle position.
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Sensor B reports throttle position.
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The ECM compares both signals.
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If the signals correlate correctly, normal operation continues.
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If the signals disagree significantly, a diagnostic code may be stored.
This monitoring helps the ECM detect a malfunctioning sensor or circuit.
What Does "Voltage Correlation" Mean?
The word correlation is the key to understanding P2135.
P2135 does not simply mean that the throttle position sensor voltage is too high or too low.
Instead, the ECM has determined that Sensor A and Sensor B are not producing the expected relationship.
A correlation problem can occur when:
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Sensor A changes but Sensor B does not.
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Sensor B changes but Sensor A does not.
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One signal suddenly drops.
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One signal suddenly rises.
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One signal becomes intermittent.
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One signal becomes stuck.
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One signal develops an electrical dead spot.
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The difference between the two signals exceeds the permitted range.
The exact voltage values and relationship must be checked against manufacturer specifications.
Where Are Throttle Position Sensors A and B Located?
On many electronic throttle control systems, Sensor A and Sensor B are integrated into the electronic throttle body.
However, the exact design varies.
Depending on the vehicle, the sensors may be:
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Integrated into the throttle body
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Part of an electronic throttle assembly
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Connected through an integrated wiring circuit
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Associated with another throttle position sensing system
Because Sensor A and Sensor B designations are manufacturer-specific, the vehicle's wiring diagram and service information should be used before testing or replacing parts.
Symptoms of P2135
The symptoms of P2135 can vary depending on the vehicle and severity of the fault.
Check Engine Light
The Check Engine Light is one of the most common symptoms.
Reduced Engine Power
The ECM may limit engine output when it detects an unsafe or unreliable throttle-position signal.
Poor Throttle Response
The engine may respond slowly or inconsistently when the accelerator is pressed.
Poor Acceleration
The vehicle may have noticeably reduced power.
Limp Mode
The vehicle may enter a protective operating mode.
Engine Hesitation
Hesitation can occur during acceleration.
Inconsistent Engine Response
Engine response may not correspond normally with accelerator input.
Engine Surging
Some vehicles may experience unstable engine-speed changes.
Rough Idle
Throttle-position problems can affect idle control.
Engine Stalling
A severe electronic throttle problem can contribute to stalling.
Cruise Control Disabled
Cruise control may be disabled when a throttle-control fault is detected.
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 P2135
Faulty Throttle Position Sensor
A defective throttle position sensor is one of the most common causes.
Possible failures include:
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Internal sensor wear
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Worn resistive track
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Signal dropout
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Dead spots
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Internal electrical failure
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Intermittent signal
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Incorrect voltage output
On many vehicles, the sensors are integrated into the throttle body and cannot be replaced separately.
Faulty Electronic Throttle Body
The electronic throttle body may develop an internal failure affecting one or both position sensor signals.
Possible problems include:
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Internal TPS failure
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Actuator motor failure
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Internal wiring damage
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Electronic circuit failure
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Throttle shaft problems
In such cases, throttle body replacement may be necessary after proper testing.
Damaged Wiring
Wiring problems can interrupt or alter one of the TPS signals.
Possible causes include:
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Chafing
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Broken wires
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Melted insulation
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Heat damage
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Engine vibration
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Corrosion
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Previous repair damage
Corroded Electrical Connectors
Corrosion can increase resistance or interrupt the sensor circuit.
Inspect for:
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Green corrosion
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White deposits
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Moisture
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Oxidized terminals
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Loose pins
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Damaged connector housings
Loose or Damaged Terminals
A connector may appear properly connected while one terminal has poor electrical contact.
Possible problems include:
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Loose terminal tension
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Bent pin
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Backed-out terminal
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Corroded contact
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Partially disconnected terminal
This can cause intermittent P2135.
Short to Ground
A sensor signal wire contacting ground can pull the voltage lower than expected.
This may cause Sensor A and Sensor B to disagree.
Short to Power
A sensor signal wire contacting a positive circuit can raise the signal voltage unexpectedly.
Possible sources include:
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Battery voltage
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Ignition power
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Another electrical circuit
Open Circuit
A broken wire or disconnected connector can interrupt one of the TPS signals.
Possible causes include:
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Broken wiring
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Damaged connector
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Failed splice
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Internal harness damage
Reference-Voltage Problems
Many throttle position sensors use a regulated reference voltage.
A problem with the reference circuit can affect sensor operation.
Possible causes include:
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Shorted sensor
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Damaged reference wire
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Wiring failure
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ECM/PCM circuit problem
Poor Sensor Ground
A poor sensor ground can change the voltage reported by the TPS.
Possible causes include:
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Corroded ground connection
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Loose terminal
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Damaged ground wire
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ECM/PCM ground problem
Low Battery or Charging-System Voltage
Electronic throttle systems can be affected by unstable system voltage.
Possible causes include:
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Weak battery
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Faulty alternator
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Poor battery terminals
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Charging-system wiring problems
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Poor engine grounds
If several unrelated electrical codes are present, the charging and grounding systems should be checked.
Throttle Plate Contamination
Carbon buildup can interfere with throttle plate movement.
Possible symptoms include:
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Sticking throttle plate
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Rough idle
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Poor acceleration
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Slow throttle response
However, carbon buildup does not automatically mean the TPS has failed. The throttle body and position signals should be tested before replacement.
Mechanical Throttle Binding
The throttle plate may fail to move smoothly because of:
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Carbon deposits
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Debris
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Damaged throttle shaft
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Mechanical damage
Mechanical binding can result in abnormal throttle-position feedback.
Incorrect Previous Repairs
Previous repairs can cause P2135 if they result in:
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Incorrect wiring
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Poor splices
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Pinched harnesses
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Damaged terminals
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Incorrect connector installation
Aftermarket Modifications
Potential sources include:
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ECU tuning
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Throttle-response devices
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Modified wiring
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Engine swaps
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Aftermarket throttle components
Poorly designed modifications can interfere with the expected relationship between TPS signals.
Faulty ECM/PCM
An ECM/PCM problem is possible, but it is generally less common than:
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Throttle position sensor failure
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Electronic throttle body failure
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Wiring problems
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Connector problems
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Reference-voltage problems
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Ground problems
The ECM/PCM should only be considered after the sensor circuits and related electrical systems have been properly tested.
Vehicles Commonly Affected by P2135
P2135 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.
P2135 can occur on any compatible vehicle when the ECM detects an abnormal voltage relationship between the relevant Throttle Position Sensor A and B signals.
Important: The exact sensor design, voltage range, and component location can vary by manufacturer and model.
How Is P2135 Diagnosed?
Proper diagnosis should determine whether the problem is caused by the throttle body, position sensors, wiring, connectors, reference voltage, ground circuit, or ECM/PCM.
Check for Additional Trouble Codes
Start with a complete diagnostic scan.
Look for:
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P2135
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Other throttle position codes
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Accelerator pedal position codes
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Throttle actuator 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
Additional codes can help identify whether the problem is electrical, mechanical, or related to the throttle assembly.
Check Freeze-Frame Data
Review the freeze-frame information recorded when P2135 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 fault occurred during:
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Idle
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Acceleration
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Cruising
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Deceleration
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Throttle movement
Monitor Live Data
Use a capable scan tool to monitor:
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Throttle Position Sensor A
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Throttle Position Sensor B
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Accelerator pedal position
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Commanded throttle position
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Actual throttle position
Slowly operate the accelerator pedal and observe the sensor values.
The signals should change smoothly and maintain their expected relationship.
Look for:
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Sudden jumps
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Dropouts
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Frozen readings
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Erratic signals
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One sensor changing while the other remains fixed
Identify the Correct TPS Circuits
Before testing with a multimeter, use the vehicle-specific wiring diagram to identify:
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TPS A signal
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TPS B signal
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Sensor reference voltage
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Sensor ground
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ECM/PCM terminals
Do not rely on generic pin assignments.
Check Battery and Charging Voltage
Verify:
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Battery condition
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Battery terminals
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Alternator operation
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Charging voltage
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Engine grounds
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Chassis grounds
Correct voltage problems before performing detailed TPS diagnosis.
Inspect the Throttle Body Connector
Check for:
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Corrosion
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Bent pins
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Loose terminals
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Water intrusion
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Damaged locking tabs
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Melted wiring
Inspect the Wiring Harness
Inspect wiring between the throttle body and ECM/PCM.
Look for:
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Chafing
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Broken insulation
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Melted wires
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Exposed conductors
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Pinched wiring
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Poor previous repairs
Pay particular attention to areas near:
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Exhaust components
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Engine mounts
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Moving components
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High-temperature areas
Check Reference Voltage
Measure the reference voltage according to manufacturer specifications.
Many systems use approximately a 5-volt reference, but this should not be assumed without checking the vehicle's specifications.
Check:
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Reference voltage
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Sensor ground
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TPS A signal
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TPS B signal
Check Sensor Ground
Verify that the sensor ground circuit has a good electrical connection.
A poor ground can cause incorrect TPS voltage readings.
Check for Short Circuits
Test the relevant circuits for:
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Short to ground
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Short to power
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Short between TPS signal circuits
Perform Voltage-Drop Testing
Voltage-drop testing can identify excessive resistance in:
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Power circuits
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Ground circuits
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Connector terminals
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Wiring splices
Test TPS Signals With a Multimeter
Depending on the manufacturer's diagnostic procedure, TPS signal voltage can be monitored while the throttle is moved.
The signal should generally change smoothly without:
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Sudden drops
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Spikes
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Dead spots
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Intermittent interruptions
The exact voltage range must be compared with manufacturer specifications.
Test the Electronic Throttle Body
If the sensors are integrated into the throttle body, test:
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Power supply
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Ground
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TPS A
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TPS B
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Throttle actuator
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Throttle movement
If internal failure is confirmed, the throttle body may require replacement.
Inspect the Throttle Plate
Check for:
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Carbon buildup
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Mechanical sticking
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Restricted movement
-
Damaged throttle plate
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Damaged throttle shaft
Check for Aftermarket Modifications
Inspect for:
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ECU tuning
-
Throttle-response devices
-
Modified wiring
-
Engine swaps
-
Non-standard throttle components
Correct or remove modifications if they are responsible for the fault.
Check ECM/PCM Power and Grounds
Verify:
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Battery power
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Ignition power
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ECM/PCM grounds
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Sensor reference circuits
How to Fix P2135
The correct repair depends on the actual cause.
Replace a Faulty Electronic Throttle Body
If testing confirms that the integrated TPS circuits or throttle actuator have failed, replacing the throttle body may be necessary.
Repair Damaged Wiring
Repair or replace wiring damaged by:
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Heat
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Chafing
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Corrosion
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Vibration
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Previous repairs
Repair or Replace Damaged Connectors
Replace damaged connector housings or terminals and ensure proper terminal tension.
Repair Reference-Voltage Problems
Repair damaged:
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Reference-voltage circuits
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Sensor grounds
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Related wiring
Repair Power and Ground Problems
Restore proper:
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Battery connections
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Engine grounds
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Chassis grounds
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ECM/PCM grounds
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Throttle-body power circuits
Repair Short Circuits
Locate and repair wiring shorted to:
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Ground
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Battery voltage
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Another electrical circuit
Clean the Throttle Body
If carbon buildup is causing mechanical sticking, clean the throttle body according to the manufacturer's procedure.
Avoid damaging the integrated sensors or electronic actuator.
Correct Previous Repairs
Repair incorrectly connected or poorly repaired wiring.
Correct Aftermarket Modifications
Restore the original throttle-control configuration when modifications are responsible for the problem.
Perform Required Relearn Procedures
Some vehicles may require:
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Throttle body relearn
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Idle relearn
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Throttle position calibration
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Electronic throttle adaptation
Use the correct manufacturer-specific procedure.
Repair or Replace the ECM/PCM
The ECM/PCM should only be considered after all relevant sensor circuits, wiring, connectors, power supplies, grounds, and reference circuits have been tested.
What Happens If P2135 Is Ignored?
Ignoring P2135 can cause continuing throttle-control problems.
Possible consequences include:
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Reduced engine power
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Poor acceleration
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Limp mode
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Engine hesitation
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Rough running
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Engine stalling
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Poor fuel economy
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Additional throttle-control codes
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Increased emissions
Because the throttle position signals are used as a safety check, the fault should not be ignored.
Can You Drive With P2135?
Driving with P2135 may be possible in some cases, but the vehicle should be diagnosed promptly.
A short trip may be possible if:
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The engine runs smoothly.
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Throttle response remains predictable.
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There is no significant loss of power.
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The vehicle is not stalling.
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The Check Engine Light is not flashing.
Avoid driving if you experience:
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Sudden power loss
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Severe reduced-power mode
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Repeated stalling
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Unpredictable throttle response
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Severe hesitation
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Flashing Check Engine Light
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Multiple warning messages
If throttle response becomes unpredictable or engine power is severely limited, the vehicle should be inspected before continued driving.
Is P2135 a Serious Code?
P2135 is generally considered a moderate to potentially high-severity diagnostic trouble code because it involves the electronic throttle position system.
The redundant throttle-position signals are designed to verify that the throttle plate is responding correctly.
When the ECM detects that Sensor A and Sensor B no longer correlate properly, it may limit engine power as a safety precaution.
The fault can affect:
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Throttle response
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Engine power
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Acceleration
-
Driveability
-
Fuel efficiency
The vehicle should be diagnosed promptly, especially when reduced-power mode or unpredictable throttle behavior is present.
How to Prevent P2135
Recommended practices include:
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Keep throttle-body connectors clean and dry.
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Repair damaged wiring promptly.
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Secure wiring harnesses away from heat and moving components.
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Maintain battery terminals.
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Maintain engine and chassis grounds.
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Address charging-system problems quickly.
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Keep the throttle body clean when appropriate.
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Avoid poorly designed throttle modifications.
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Avoid low-quality electrical repairs.
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Inspect wiring after major engine repairs.
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Use correct replacement parts.
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Do not ignore Check Engine Light warnings.
P2135 vs. Related Codes
| Code | General Description |
|---|---|
| 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 primary difference is the specific pair of sensor signals being compared.
P2135 specifically identifies a voltage correlation problem between Throttle Position Sensor A and Sensor B.
Final Thoughts
The P2135 Throttle Position Sensor A/B Voltage Correlation diagnostic trouble code indicates that the ECM/PCM has detected that Throttle Position Sensor A and Throttle Position Sensor B are no longer maintaining their expected electrical relationship.
Common causes include:
-
Faulty throttle position sensor
-
Faulty electronic throttle body
-
Internal TPS failure
-
Damaged wiring
-
Corroded connectors
-
Loose terminals
-
Short circuits
-
Open circuits
-
Reference-voltage problems
-
Poor sensor grounds
-
Low system voltage
-
Throttle plate contamination
-
Mechanical throttle binding
-
Incorrect previous repairs
-
Aftermarket modifications
-
ECM/PCM faults
The most important diagnostic step is to identify the correct TPS A and TPS B circuits for the specific vehicle.
A capable scan tool can be used to monitor both signals while the throttle is operated. The signals should change smoothly and maintain the relationship specified by the manufacturer.
The wiring, connectors, reference voltage, sensor ground, power supply, and throttle-body operation should be tested before replacing expensive components.
P2135 does not automatically mean that the throttle body needs to be replaced. A damaged wire, poor connector, bad ground, reference-voltage problem, or intermittent electrical connection can produce the same code.
Finding the actual reason why the TPS A and TPS B signals no longer correlate correctly is essential for restoring reliable throttle operation, proper engine performance, and safe vehicle driveability.
