Code
P2138
MITSUBISHI
P — Powertrain
APS(main/sub) correlation
Views:
UK: 28
EN: 44
RU: 97
AI status
Completed
Completed
100%
Causes
- Faulty accelerator pedal position sensor (main or sub)
- Damaged, corroded or loose wiring/connector at the pedal or ECU
- Open/shorted signal, reference or ground circuit
- Loss or instability of the 5 V reference from the ECU
- Intermittent connector contact (water intrusion, corrosion)
- Aftermarket throttle controller or modification interfering with signals
Symptoms
- MIL/Check Engine lamp on
- Reduced engine power / limp-home mode
- Poor throttle response, hesitation or inconsistent acceleration
- Pedal position readings on scan tool show mismatch between main and sub
- DTC may reappear intermittently, especially after moisture or movement
What to check
- Read and record all stored and pending DTCs and freeze frame data using a scan tool
- Visually inspect accelerator pedal assembly, connector and harness for damage, corrosion or water ingress
- Scan live data for APS (main and sub) while key on and while operating pedal — look for smooth correlated movement
- Check for related codes (5 V reference, ground, or throttle actuator codes)
- Wiggle test wiring while monitoring live data to find intermittent wiring faults
Signal parameters
- Both APS outputs should change smoothly and predictably as pedal is moved (no sudden jumps or dropouts)
- Typical APS behavior: low voltage at rest, rising voltage with pedal travel; full travel values commonly near the upper end of sensor range (manufacturer-specific; often ~0.5–4.5 V)
- 5 V reference from ECU present and stable at sensor connector
- Signal wires should show continuity to ECU pins and signal voltages should correlate within manufacturer threshold
Diagnostic algorithm
- Connect a scan tool, record P2138 and any related codes, and observe freeze frame data.
- Monitor live data for APS main and sub with ignition on and with engine running (if safe). Note voltages/percentages at rest and during full pedal travel — check for smooth, correlated response.
- Visually inspect pedal harness and connector for damage, corrosion, loose pins or water; repair any obvious faults.
- Backprobe the pedal connector: verify 5 V reference present, signal outputs move with pedal, and ground continuity. Compare measured voltages to live data on the scan tool.
- Perform continuity and resistance checks from pedal connector to ECU pins; repair any opens/shorts or high resistance connections.
- Wiggle wiring and connectors while watching live data to find intermittent faults.
- If wiring and connectors are good but signals remain uncorrelated, replace the accelerator pedal assembly (both sensors).
- If replacement pedal does not correct the issue, consider testing/replacing the PCM or consult manufacturer service information for specific ECM tests.
- After repairs, clear codes, perform a road test and recheck for return of the DTC.
Likely causes
- Failed APS sub sensor (most common)
- Broken or chafed harness between pedal and ECU
- Pin corrosion or bent pin in pedal connector
- Faulty ground or 5 V reference wiring
- Intermittent wiring fault revealed by vibration or pedal movement
Fault status
Status
APS (main/sub) correlation fault — accelerator pedal sensor outputs disagree; ECU stored code and may limit engine power.
Repair difficulty: Medium
Diagnostic time: 0.5–2.0 hours
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