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P2138 Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation
The P2138 Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation diagnostic trouble code indicates that the Engine Control Module (ECM/PCM) has detected that two position-related signals identified as D and E are not maintaining the expected voltage relationship.
In simple terms, the vehicle's computer compares two electronic throttle or accelerator pedal position signals and has determined that they do not agree with each other as expected.
Modern electronic throttle control systems use multiple sensors for safety and accuracy. The ECM continuously compares the signals. If the relationship between Sensor D and Sensor E becomes inconsistent, P2138 may be stored.
Depending on the vehicle, P2138 may cause the Check Engine Light, reduced engine power, poor throttle response, hesitation, limp mode, poor acceleration, engine surging, rough running, or other electronic throttle control problems.
The exact meaning and location of Sensors D and E vary by manufacturer. They may be located in the accelerator pedal assembly, electronic throttle body, or another related position-sensing system.
What Does P2138 Mean?
P2138 means that the ECM/PCM has detected an incorrect correlation between two position-related sensor signals identified as D and E.
The ECM does not necessarily expect the two sensors to produce identical voltages.
Instead, it expects them to maintain a specific relationship.
For example:
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Both sensor voltages may increase as pedal position increases.
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The two sensors may operate over different voltage ranges.
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One signal may increase while the other decreases.
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One signal may operate at a different rate or scale.
As long as the relationship remains within the manufacturer's programmed limits, the system operates normally.
If the difference becomes too large, one signal becomes erratic, or the expected relationship is lost, the ECM may store P2138.
Why Are Multiple Throttle and Pedal Sensors Used?
Modern electronic throttle systems use redundant sensors for safety.
The accelerator pedal often does not directly operate the throttle plate mechanically.
Instead:
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The driver presses the accelerator pedal.
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Position sensors detect pedal movement.
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The ECM compares multiple sensor signals.
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The ECM determines the requested engine power.
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The ECM commands the electronic throttle actuator.
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Throttle position sensors report actual throttle movement.
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The ECM continuously compares the signals.
Multiple sensors allow the ECM to identify sensor disagreement.
This is an important safety feature because an incorrect throttle signal could create unsafe engine-power behavior.
What Does "Voltage Correlation" Mean?
A voltage correlation code means that the relationship between two signals is incorrect.
It does not necessarily mean that both sensors have a low or high voltage.
For example, when the accelerator pedal is pressed:
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Sensor D should follow its programmed voltage pattern.
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Sensor E should follow its own expected pattern.
The ECM compares the signals continuously.
A correlation fault may occur when:
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One signal changes but the other does not.
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One signal drops out.
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One signal suddenly jumps.
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One signal becomes intermittent.
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One signal remains fixed.
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The difference between signals becomes too large.
Where Are Sensors D and E Located?
The exact location depends on the vehicle.
The affected sensors may be:
Inside the accelerator pedal assembly
Many electronic accelerator pedals contain multiple internal position sensors.
Inside the electronic throttle body
The throttle body may contain multiple throttle position sensors.
Part of another throttle-position sensing system
The exact D/E circuit identification should be confirmed using manufacturer service information.
Do not assume that Sensors D and E are always located in the same component.
Symptoms of P2138
The symptoms vary depending on the vehicle and severity of the fault.
Check Engine Light
The Check Engine Light is the most common symptom.
Reduced Engine Power
The ECM may activate reduced-power mode.
Poor Throttle Response
The vehicle may respond slowly to accelerator pedal input.
Poor Acceleration
Acceleration may be significantly reduced.
Limp Mode
The ECM may limit throttle operation as a safety precaution.
Engine Hesitation
The vehicle may hesitate during acceleration.
Inconsistent Acceleration
Engine response may feel irregular.
Engine Surging
Some vehicles may experience unstable throttle response.
Rough Idle
Idle quality may be affected.
Engine Stalling
Severe electronic throttle faults can contribute to stalling.
Cruise Control Problems
Cruise control may be disabled.
Additional Warning Messages
Depending on the vehicle, messages may include:
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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 P2138
Faulty Accelerator Pedal Position Sensor
The accelerator pedal assembly may contain multiple sensors.
If one internal signal no longer matches the others, P2138 can be stored.
Possible problems include:
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Internal sensor wear
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Electrical failure
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Signal dropout
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Contamination
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Incorrect internal resistance
Many vehicles require replacement of the complete accelerator pedal assembly.
Faulty Electronic Throttle Body
The electronic throttle body may contain:
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Multiple throttle position sensors
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An actuator motor
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Internal control electronics
Possible faults include:
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Internal sensor failure
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Actuator failure
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Damaged internal electronics
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Incorrect position feedback
Damaged Wiring
Damaged wiring may affect one signal while another continues operating normally.
Possible causes include:
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Chafed wiring
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Broken wires
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Melted insulation
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Exhaust heat damage
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Corrosion
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Engine vibration
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Previous repairs
Corroded Electrical Connectors
Corrosion can cause incorrect or unstable sensor readings.
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 connected while an internal terminal is:
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Loose
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Bent
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Corroded
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Backed out
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Partially disconnected
This can cause intermittent correlation problems.
Short to Ground
A sensor signal wire may contact:
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Chassis ground
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Engine metal
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Another ground circuit
This can pull one sensor voltage lower than expected.
Short to Power
A sensor wire may contact:
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Battery voltage
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Ignition power
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Another positive electrical circuit
This can force one sensor signal higher than expected.
Open Circuit
A broken or disconnected wire can interrupt one of the sensor 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 and pedal sensors use a regulated reference voltage.
A reference-voltage problem can affect multiple sensor readings.
Possible causes include:
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Shorted sensor
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Damaged reference-voltage wiring
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Wiring problem
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ECM/PCM circuit failure
Poor Sensor Ground
A poor ground can change the voltage reported by a sensor.
Possible causes include:
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Corroded ground wiring
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Loose connector
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Damaged sensor ground
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ECM/PCM ground problem
Low Battery or Charging-System Voltage
Low system voltage can affect electronic throttle operation.
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
Throttle Plate Contamination
Carbon deposits can interfere with throttle movement.
Possible symptoms include:
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Sticking throttle
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Rough idle
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Poor acceleration
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Reduced engine response
Carbon buildup alone does not normally cause a voltage correlation code unless mechanical sticking causes abnormal position feedback.
Mechanical Throttle Binding
The throttle plate may not move freely because of:
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Carbon buildup
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Mechanical damage
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Debris
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Damaged throttle shaft
This can cause the position feedback to become inconsistent.
Incorrect Previous Repairs
Previous repairs may have caused:
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Incorrect wiring connections
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Poor splices
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Pinched wiring
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Damaged terminals
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Incorrect connector installation
Aftermarket Modifications
Possible modifications include:
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ECU tuning
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Pedal controllers
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Throttle-response devices
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Engine swaps
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Modified wiring harnesses
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Aftermarket engine electronics
These can sometimes affect sensor correlation.
Faulty ECM/PCM
An ECM/PCM problem is possible but less common than:
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Sensor failure
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Throttle body failure
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Pedal assembly failure
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Wiring damage
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Connector problems
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Reference-voltage faults
The ECM/PCM should only be considered after external circuits are properly tested.
Vehicles Commonly Affected by P2138
P2138 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.
P2138 is more likely to occur on vehicles using electronic throttle control and multiple redundant position sensors.
How Is P2138 Diagnosed?
The purpose of diagnosis is to determine what Sensors D and E represent on the specific vehicle and why their signals no longer correlate correctly.
Check for Additional Trouble Codes
Perform a complete diagnostic scan.
Look for:
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P2138
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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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Battery-voltage codes
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Communication codes
Related codes can provide important diagnostic information.
Check Freeze-Frame Data
Review the conditions recorded when P2138 was stored.
Useful information includes:
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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 when the correlation problem occurs.
Identify Sensors D and E
This is one of the most important diagnostic steps.
Use manufacturer service information to identify:
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The component associated with Sensor D
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The component associated with Sensor E
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Their expected voltage ranges
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Their expected relationship
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Relevant ECM/PCM terminals
Do not assume that the letters have the same meaning on every vehicle.
Monitor Live Data
Use a capable scan tool to monitor:
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Accelerator pedal position
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Throttle position
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Sensor D signal
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Sensor E signal
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Commanded throttle position
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Actual throttle position
Slowly operate the accelerator pedal while observing the sensor values.
The signals should:
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Change smoothly
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Remain stable
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Maintain the expected relationship
Look for:
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Signal dropouts
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Sudden jumps
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Frozen readings
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Erratic changes
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One signal changing while another remains fixed
Check Battery and Charging Voltage
Verify:
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Battery condition
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Battery terminal connections
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Alternator output
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Charging voltage
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Engine and chassis grounds
Repair system-voltage problems before continuing with detailed sensor diagnosis.
Inspect the Accelerator Pedal Connector
Check for:
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Corrosion
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Loose terminals
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Bent pins
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Water intrusion
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Damaged locking tabs
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Backed-out terminals
Inspect the Throttle Body Connector
Check for:
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Corrosion
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Heat damage
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Loose terminals
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Broken wiring
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Oil contamination
Inspect Wiring Harnesses
Inspect wiring between:
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Accelerator pedal and ECM
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Throttle body and ECM
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Position sensors and ECM/PCM
Look for:
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Chafing
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Broken insulation
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Melted wiring
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Exposed conductors
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Previous repairs
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Pinched harnesses
Check Reference Voltage
Measure the relevant reference voltage according to manufacturer procedures.
Many systems use approximately a 5-volt reference.
Check:
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Reference voltage
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Sensor ground
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Sensor output
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Wiring continuity
Check for Short Circuits
Inspect for:
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Short to ground
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Short to power
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Short between sensor wires
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Internal component short
A short circuit can cause one sensor to move outside the expected D/E relationship.
Perform Voltage-Drop Testing
Voltage-drop testing can help locate 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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Splices
Test the Accelerator Pedal Assembly
If the D/E circuits are located in the accelerator pedal assembly, test the internal sensors according to manufacturer specifications.
If one sensor fails, the complete pedal assembly may require replacement.
Test the Electronic Throttle Body
If the affected circuits are located in the throttle body, test:
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Power supply
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Ground
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Throttle position sensors
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Actuator motor
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Position feedback
Compare results with manufacturer specifications.
Inspect the Throttle Plate
If electrical tests are normal, inspect the throttle body for:
-
Carbon buildup
-
Mechanical sticking
-
Damaged throttle plate
-
Restricted movement
Check for Aftermarket Modifications
Inspect:
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Pedal controllers
-
ECU tuning
-
Throttle-response devices
-
Modified wiring
-
Engine swaps
Incorrect modifications can affect sensor correlation.
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 P2138
The correct repair depends on the cause identified during diagnosis.
Replace a Faulty Accelerator Pedal Assembly
If internal pedal position sensors are defective, replacement of the complete pedal assembly may restore proper correlation.
Replace a Faulty Electronic Throttle Body
If testing confirms internal throttle position sensor or actuator failure, replace the throttle body or applicable component.
Repair Damaged Wiring
Repair or replace wiring damaged by:
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Heat
-
Chafing
-
Corrosion
-
Vibration
-
Previous repairs
Repair or Replace Damaged Connectors
Replace damaged connector housings or terminals and ensure correct terminal tension.
Repair Reference-Voltage Problems
Repair damaged:
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Reference-voltage wiring
-
Sensor ground circuits
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Related sensor circuits
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 actuator power circuits
Repair Short Circuits
Locate and repair wires 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 affecting throttle movement, clean the throttle body according to manufacturer procedures.
Avoid damaging electronic sensors or actuator components.
Correct Previous Repairs
Restore the original wiring configuration if previous repairs caused the fault.
Correct Aftermarket Modifications
Restore the throttle-control system to the correct manufacturer configuration when modifications are responsible for the fault.
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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Accelerator pedal calibration
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Electronic throttle adaptation
Use the correct manufacturer procedure.
Repair or Replace the ECM/PCM
The ECM/PCM should only be considered after all sensors, wiring, connectors, power supplies, grounds, and reference circuits have been properly tested.
What Happens If P2138 Is Ignored?
Ignoring P2138 can cause continuing throttle-control problems.
Possible consequences include:
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Reduced engine power
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Poor acceleration
-
Limp mode
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Engine hesitation
-
Rough running
-
Engine stalling
-
Poor fuel economy
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Additional throttle-control codes
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Increased emissions
Because sensor correlation is an important safety function, the fault should not be ignored.
Can You Drive With P2138?
Driving with P2138 may be possible, but the vehicle should be diagnosed promptly.
A short drive 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 major 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 reduction in engine power
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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
Is P2138 a Serious Code?
P2138 is generally considered a moderate to potentially high-severity diagnostic trouble code because it involves electronic throttle and accelerator pedal position signals.
Modern vehicles use redundant sensor signals for safety.
When the ECM detects that two position signals no longer correlate correctly, it may reduce engine power to prevent unsafe throttle operation.
The fault can affect:
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Throttle response
-
Engine power
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Acceleration
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Driveability
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Fuel efficiency
The vehicle should be diagnosed promptly, especially when reduced-power mode is active.
How to Prevent P2138
Recommended practices include:
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Keep electrical connectors clean and dry.
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Repair damaged wiring promptly.
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Secure wiring harnesses correctly.
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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.
P2138 vs. Related Codes
| Code | General Description |
|---|---|
| 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 |
| P2137 | Throttle/Pedal Position Sensor/Switch C/E Voltage Correlation |
| P2136 | Throttle/Pedal Position Sensor/Switch C/D Voltage Correlation |
| P2135 | Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation |
The main difference is the specific pair of sensor signals being compared.
P2138 relates specifically to the expected relationship between Sensor D and Sensor E.
Final Thoughts
The P2138 Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation diagnostic trouble code indicates that the ECM/PCM has detected that two position-related signals identified as D and E are no longer maintaining their expected electrical relationship.
Common causes include:
-
Faulty accelerator pedal position sensor
-
Faulty electronic throttle body
-
Internal sensor 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
Correct diagnosis begins by identifying what Sensors D and E represent on the specific vehicle.
A capable scan tool should then be used to compare live sensor data while the accelerator pedal and throttle position change.
The wiring, connectors, power supply, grounds, and reference-voltage circuits should also be tested before replacing expensive components.
P2138 does not automatically mean that the accelerator pedal assembly or throttle body must be replaced. A damaged wire, corroded connector, poor sensor ground, reference-voltage fault, or another electrical problem can produce the same correlation failure.
Finding the exact reason why the D and E signals no longer agree is essential for restoring safe throttle operation, proper engine performance, and reliable vehicle driveability.
