P2138 Code: Throttle/Pedal Position Sensor D/E Voltage Correlation

The P2138 diagnostic trouble code (DTC) is triggered when your vehicle’s engine control module (ECM) detects a voltage mismatch between two throttle or pedal position sensors. Modern vehicles use redundant sensors for safety—typically sensors D and E—that should report nearly identical positions. When these signals diverge beyond an acceptable threshold, your check engine light illuminates and this code is stored.

What Does P2138 Mean?

P2138 stands for “Throttle/Pedal Position Sensor D/E Voltage Correlation.” Here’s the technical breakdown:

• P: Powertrain code
• 2: Generic OBD-II code (applies to all manufacturers)
• 1: Fuel and air metering system
• 38: Throttle/Pedal Position Sensor D/E Voltage Correlation

Modern vehicles use dual or redundant throttle position sensors as a safety feature. Sensor D and Sensor E monitor the same throttle blade or accelerator pedal position and should produce nearly identical voltage outputs. The ECM continuously compares these signals. If the voltage difference exceeds the manufacturer’s specification (typically 10-15% variance), the code P2138 is triggered.

This is a serious code because the ECM cannot trust the accelerator input, which is critical for engine control, emissions management, and vehicle safety. The vehicle may enter “limp mode” to protect itself and the driver.

Common Symptoms

• Check Engine Light: The illuminated MIL (Malfunction Indicator Lamp) is the primary indicator
• Reduced Engine Power: Vehicle enters limp mode with limited acceleration
• Sluggish Acceleration: Engine hesitates or feels unresponsive when pressing the gas pedal
• Stalling: Engine may stall at idle or during acceleration
• Difficulty Starting: Engine cranks but has trouble catching
• Erratic Idle: RPM fluctuates unpredictably at stops
• No Acceleration Response: Pedal feels “dead” or unresponsive
• Transmission Issues: Automatic transmissions may shift erratically or refuse to shift

Possible Causes (Ranked by Frequency)

1. Faulty Throttle Position Sensor (TPS) – The most common cause. One of the two sensors (D or E) is failing internally or producing incorrect voltage signals.
2. Accelerator Pedal Position Sensor Malfunction – In drive-by-wire systems, the pedal sensor itself may be defective or worn.
3. Corroded or Loose Electrical Connectors – Connector corrosion, loose pins, or poor contact can cause voltage fluctuations that trigger the code.
4. Damaged Wiring Harness – Frayed, pinched, or damaged wires between the sensor and ECM can cause signal interference or voltage drops.
5. Water Intrusion or Moisture – Moisture in the sensor housing or connector can cause intermittent electrical faults.
6. Engine Control Module (ECM) Failure – Rarely, the ECM itself may malfunction and misinterpret correct sensor signals. This is typically a last-resort diagnosis.
7. Vacuum Leaks – In older throttle cable systems, vacuum leaks can affect sensor readings indirectly.
8. Throttle Blade Binding – A stuck or binding throttle blade may cause inconsistent sensor readings.

Diagnostic Steps

Step 1: Retrieve and Document the Code

Use an OBD-II scanner to read the code and any related codes. Document the freeze frame data (engine speed, load, fuel trim, etc.) as this provides context about when the fault occurred.

Step 2: Visual Inspection

• Inspect the accelerator pedal for physical damage, binding, or loose components
• Check the throttle body for carbon buildup or debris
• Examine all wiring harnesses and connectors for corrosion, loose pins, or damage
• Look for water intrusion or moisture in sensor connectors

Step 3: Clean Connectors and Terminals

Disconnect the sensor connectors and inspect the pins. Use electrical contact cleaner and a small brush to remove corrosion. Reconnect firmly and test-drive to see if the code clears. This simple step resolves the issue in many cases.

Step 4: Measure Sensor Voltages

Using a digital multimeter set to DC voltage, measure the output of both throttle position sensors (D and E) while the ignition is on but the engine off. Then have an assistant gently press the accelerator pedal while you observe the voltage changes. Both sensors should track closely together. A significant divergence indicates a faulty sensor.

Step 5: Check Wiring Continuity

Set your multimeter to resistance (ohms) mode and check for continuity along the wiring harness from each sensor to the ECM. Any breaks or high resistance indicate damaged wiring that needs repair or replacement.

Step 6: Test Under Load

Clear the code and take the vehicle on a test drive, accelerating moderately. If the code returns immediately, the fault is constant. If it returns intermittently, you may have a connector issue that only occurs under specific conditions (heat, vibration, etc.).

Step 7: Replace the Faulty Sensor

If diagnostics point to a specific sensor, replace it with an OEM or quality aftermarket part. Always replace both sensors together if one is faulty, as they are designed to work as a matched pair.

Step 8: Clear the Code and Verify

After repairs, clear the code using your scanner and perform a test drive to confirm the fix. The code should not return.

Repair Cost Estimates

DIY Repairs (if you have mechanical skills):

• Connector cleaning and corrosion removal: $0-$50 (parts only)
• Single throttle position sensor replacement: $50-$200 (sensor cost)
• Accelerator pedal sensor replacement: $100-$300 (sensor cost)

Professional Mechanic Repairs:

• Diagnostic scan and connector cleaning: $100-$200
• Single sensor replacement (labor + parts): $200-$500
• Both sensors replacement (labor + parts): $400-$800
• Wiring harness repair or replacement: $300-$1,000+ (depending on extent of damage)
• ECM reprogramming or replacement: $1,500-$3,000+ (rare, only if ECM is faulty)

Dealership Repairs:

Expect to pay 20-40% more at a dealership compared to independent shops, typically ranging from $500-$1,200 for sensor replacement and diagnostics.

Can I Still Drive?

Safety Assessment: Proceed with Caution

While you may be able to drive a vehicle with code P2138, it’s not recommended for extended periods. Here’s why:

• Limp Mode: Your vehicle will likely operate in reduced-power mode, limiting acceleration and highway merging capability
• Unpredictable Behavior: The engine may stall, hesitate, or respond erratically to throttle input, creating safety hazards
• Transmission Issues: Automatic transmissions may shift harshly or refuse to shift, affecting drivability
• Emissions: The vehicle may produce excess emissions and fail an emissions test

Recommendation: Have the vehicle diagnosed and repaired as soon as possible. If you must drive it, avoid heavy traffic, highway speeds, and extended trips. Do not ignore this code, as it indicates a safety-critical system malfunction.

Frequently Asked Questions

Q: Can a bad battery cause code P2138?

A: Indirectly, yes. A weak or failing battery can cause voltage fluctuations that affect sensor readings. However, a battery issue would typically trigger other codes first. If you have a weak battery, replace it and retest before replacing sensors.

Q: Will code P2138 go away on its own?

A: No. This code requires a repair to the throttle/pedal position sensor system. The code will remain stored and the check engine light will stay illuminated until the underlying problem is fixed and the code is cleared with a scanner.

Q: Is P2138 the same as P0122 or P0123?

A: No. P0122 is “Throttle/Pedal Position Sensor A Circuit Low,” P0123 is “Throttle/Pedal Position Sensor A Circuit High,” and P2138 is specifically about voltage correlation between sensors D and E. Each code points to a different problem, though they may be related to the same component.

Q: Can I drive to the mechanic with code P2138?

A: Yes, you can typically drive to a nearby mechanic for diagnosis and repair. However, avoid heavy acceleration, highway driving, and stop-and-go traffic if possible. The vehicle’s reduced power and unpredictable throttle response could create hazardous situations in demanding driving conditions.

Q: Do I need to replace both sensors if only one is faulty?

A: It’s recommended to replace both sensors together. They are designed as a matched pair and should have identical response characteristics. Replacing only one may lead to continued correlation issues or premature failure of the remaining sensor.