The P2138 code typically points to a mismatch between the throttle/pedal position sensor channels D and E in vehicles with electronic throttle control. It is often caused by faulty sensors, wiring issues, or an ECU fault.
Understanding what P2138 means
P2138 is a diagnostic trouble code indicating a voltage correlation fault between the throttle/pedal position sensor inputs labeled D and E. Modern drive-by-wire systems rely on precise readings from multiple position sensors. When the PCM detects that these two signals are out of spec or not in sync, it stores P2138 and may trigger the check engine light. Depending on the vehicle, this can affect throttle response, acceleration, or cause a limp mode until the issue is addressed.
Common causes
The following issues frequently trigger P2138, and they generally fall into sensor, wiring, or ECU categories.
- Faulty throttle position sensor (TPS) or pedal position sensor (PPS) or a sensor pair that has drifted out of calibration.
- Damaged or corroded wiring and connectors between the sensors and the PCM/ECU (loose pins, broken wires, moisture intrusion).
- Electrical supply problems such as a weak battery, poor ground, or voltage irregularities affecting sensor readings.
- PCM/ECU fault or software issue (outdated calibration, corrupted software, or a defective processor).
- Mechanical issues in the throttle body or pedal assembly causing inconsistent readings (sticking throttle plate, worn linkage).
- Unmatched aftermarket sensors or non-OEM parts that don't align with the ECU’s expected signal characteristics.
- Transient electrical noise or grounding problems that temporarily disrupt sensor signals.
In practice, diagnosing P2138 begins with conesensing sensor integrity and wiring, then confirming that the ECU is receiving clean, within-spec signals from both D and E channels.
Diagnostic steps
A systematic approach helps confirm the root cause and minimize unnecessary repairs.
- Scan the vehicle for related codes and view live data for the D and E sensor signals to see if they are in range and properly correlated.
- Inspect the wiring harnesses and connectors between the sensors and the PCM for damage, corrosion, or loose pins; reseat or replace as needed.
- Measure sensor voltages with a multimeter or use a capable scan tool to compare D and E readings across the operating range; note any anomalies or drift.
- Check for mechanical issues in the throttle body and pedal assembly, including throttle plate binding, stuck return springs, or misalignment.
- Verify battery health and charging system; ensure grounds are clean and secure to prevent voltage fluctuations.
- Consider sensor replacement if tests indicate a faulty TPS/PPS or a calibration drift that cannot be corrected.
- If sensors and wiring test normal, consult the manufacturer for ECU-related updates or reflash; in rare cases, PCM replacement may be warranted.
After completing these steps, clear the codes and perform a road test to confirm whether P2138 returns. If it does, escalate to component replacement or professional diagnosis as appropriate.
Typical fixes
Fixes depend on the diagnosed root cause, but these are common repair paths for P2138.
- Replace or recalibrate faulty throttle position sensor (TPS) and/or pedal position sensor (PPS) assemblies.
- Repair damaged wiring or replace connectors; restore proper grounding and secure routing to avoid future wear.
- Update or reflash the vehicle’s PCM/ECU software as recommended by the manufacturer.
- Address mechanical issues in the throttle body or pedal mechanism (cleaning, lubrication, or replacement of worn parts).
- Replace with OEM-compatible sensors if aftermarket parts caused signal discrepancies.
Once repairs are completed, reset the codes and test drive to ensure the P2138 code does not return. If the issue persists, a deeper diagnostic by a qualified technician may be required, potentially including PCM testing or replacement.
Summary
P2138 signals a correlation fault between the D and E throttle/pedal position sensor inputs in drive-by-wire systems. Causes typically involve sensor faults, wiring/connectors, or ECU/software issues. A methodical diagnostic — focusing on sensor signals, wiring integrity, and mechanical conditions — guides effective fixes and helps restore normal throttle performance.
How can I reset my throttle position sensor?
Method 2: Reset TPS Without a Scanner (Manual Method)
- Turn the ignition off.
- Reconnect the battery terminal securely.
- Without starting the engine, turn the ignition key to the "ON" position (all dashboard lights on).
- Slowly press the accelerator pedal to the floor, hold it for 10 seconds, then release.
How much does it cost to fix a P2138 code?
On a 2005-2012 Chevrolet Malibu, code P2138 is most often caused by a faulty Accelerator Pedal Position (APP) sensor or a wiring issue at the IP-to-body harness connector (X206). Replacing the accelerator pedal assembly is the most common fix, costing around $50-$100 for an aftermarket part.
What are common fixes for a P2138 code?
With that said, a technician will begin by replacing the throttle body motor or the throttle body assembly if it's defective or damaged. They may also repair or replace any wiring associated with the throttle body motor.
Can a bad battery cause P2138?
It's possible that low-voltage issues could be causing code P2138 to set. On your car, when the battery voltage drops below 10 volts (or the battery is disconnected, or power to the ECM is lost), the throttle body's basic setting may be lost.