P2138
Accelerator Pedal Position (APP) Sensor 1/2 Voltage Correlation
When a vehicle powertrain module registers the fault code P2138, it points directly to an internal system malfunction identified as "Accelerator Pedal Position (APP) Sensor 1/2 Voltage Correlation". Operating your engine under this condition may degrade long-term fuel maps.
Driver's Summary
Code P2138 means your vehicle detected a problem with the accelerator pedal position (app) sensor 1/2 voltage correlation system. In practice, this fault causes reduced engine power, erratic throttle behavior, limp mode. Stop driving as soon as it is safe to do so. This fault can lead to expensive secondary damage if left unaddressed.
Symptoms
Reduced engine power, erratic throttle behavior, limp mode
Common Causes
- Defective APP sensor
- Wet or corroded floor harness
- Damaged pedal wiring
- Faulty PCM
How to Fix
- 1 Replace pedal assembly
- 2 Dry out floor wiring harness
- 3 Clean APP sensor connector
- 4 Test pedal sensor voltages
Technical Explanation
The ECM detects code P2138 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The control module samples the circuit continuously during normal operation, using both voltage level monitoring and frequency analysis to detect open circuits, shorts to ground, shorts to battery voltage, and high-resistance connections. The fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
Driving with an active P2138 fault risks accelerating damage to defective app sensor and related components. The longer the fault persists, the more expensive the eventual repair becomes — what starts as a sensor or solenoid issue can escalate to major mechanical failure.
Mechanic's Pro Tip
Before replacing any component on P2138, spend 5 minutes inspecting the wiring harness and connector first — corrosion, chafed insulation, and backed-out pins cause the majority of these faults and cost nothing to fix. Use a multimeter to measure voltage drop across the connector pins under load; anything above 0.1V indicates excessive resistance that will cause intermittent failures even after replacing the sensor.
Pedal sensor/assembly: $200 - $500