P2138 — Throttle/Pedal Position Sensor 'D'/'E' Voltage Correlation

Quick answer

• What the code means: The P2138 code indicates a discrepancy between the voltage signals from two separate accelerator pedal position (APP) sensors, suggesting a fault in the electronic throttle control system.
• Severity: Get towed or cease driving immediately. This code can lead to unpredictable engine behavior, including sudden acceleration or reduced power, making the vehicle unsafe to operate.
• Most common cause: A faulty accelerator pedal position sensor or its associated wiring.

What the P2138 code means

The official OBD-II definition for P2138 is "Throttle/Pedal Position Sensor 'D'/'E' Voltage Correlation." In simpler terms, your vehicle's engine control module (ECM) or powertrain control module (PCM) has detected an inconsistency in the voltage signals received from two of the accelerator pedal position (APP) sensors, typically labeled "D" and "E." Modern vehicles use an electronic throttle control (ETC) system, also known as "drive-by-wire," which eliminates the mechanical cable connecting the accelerator pedal to the throttle body. Instead, sensors on the accelerator pedal convert pedal movement into electrical signals, which are then sent to the ECM/PCM. The ECM/PCM then uses these signals to command the throttle body to open or close, regulating engine air intake. To ensure safety and reliability, these systems often employ multiple redundant sensors (usually two or even three) that provide slightly different, but still correlated, voltage outputs as the pedal is pressed. The ECM/PCM continuously monitors these signals. If the voltage outputs from sensor "D" and sensor "E" deviate from their expected correlation for a certain period, the ECM/PCM will set the P2138 code, illuminate the check engine light, and often put the vehicle into "limp home" mode, which limits engine power and speed to prevent damage.

Common symptoms

• Check Engine Light illuminated
• Reduced engine power or "limp home" mode activation
• Hesitation or surge during acceleration
• Unresponsive accelerator pedal
• Engine stalling
• Vehicle may not accelerate above a certain speed
• Engine may go into a "fail-safe" mode, resulting in very limited power and speed.

Common causes

1. Faulty Accelerator Pedal Position (APP) Sensor: This is the most common culprit. Over time, the internal components of the sensor can wear out, leading to intermittent or incorrect voltage signals. Or the sensor can just fail. Given the constant use, this is a part that definitely experiences wear and tear.
2. Damaged or corroded wiring/connectors: Open circuits, shorts, or poor connections in the APP sensor wiring harness or its connectors can disrupt the voltage signals, causing the ECM/PCM to detect a correlation issue. Animals chewing on wires or road debris can cause damage.
3. Faulty Throttle Position Sensor (TPS) or Throttle Body: While less common than an APP sensor issue, a problem with the TPS or the electronic throttle body itself (e.g., sticking throttle plate, motor issue) can sometimes indirectly trigger P2138 if the ECM/PCM cannot get accurate feedback from the throttle in relation to the pedal input.
4. Wiring issues between the APP sensor and the ECM/PCM: Less likely than issues directly at the sensor or throttle body, but still a possibility, especially in older vehicles or those with a history of electrical work.
5. Faulty Engine Control Module (ECM) or Powertrain Control Module (PCM): This is very rare. The ECM/PCM is robust and designed to last the life of the vehicle. However, if all other possibilities have been thoroughly ruled out, a failing ECM/PCM could be the cause, though it