OBD-II trouble code
P2138: Throttle/Pedal Position Sensor 'D'/'E' Voltage Correlation
The two sensors inside the accelerator pedal don't agree with each other. Pedal-side mirror of P2135 — same correlation logic, but the failure is in the pedal under the dash, not in the throttle body. No cleaning will fix this one.
Quick facts
- System
- Powertrain
- Category
- Throttle / Idle
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $500
- DIY difficulty
- Intermediate DIY
What does P2138 mean?
P2138 is the pedal-side correlation code, structurally identical to P2135 but on the opposite end of the drive-by-wire system. The accelerator pedal contains two independent position sensors ('D' and 'E' on most platforms, or 'A' and 'B' on others), reporting to the PCM on separate signal wires with separate references. The PCM continuously compares the two readings. When they disagree by more than a programmed threshold for long enough, P2138 sets and the vehicle enters reduced-power mode.
The critical difference between P2138 and P2135 is the repair location. P2135 sends the diagnosis to the throttle body, where the most common fix is a cheap throttle body cleaning. P2138 sends the diagnosis to the pedal assembly under the dash, where cleaning isn't an option — the pedal is a sealed unit with integrated electronics, and the fix when the pedal is the failure is replacement. That makes P2138 a more expensive repair on average than P2135, even though the underlying problem (two sensors disagreeing) is structurally the same.
The most common cause is wear inside the pedal sensors. Both sensors are integrated into the pedal assembly and age together, but they don't necessarily age identically — the contact wipers or Hall-effect elements inside one sensor can develop drift, dead spots, or non-linear response while the other stays fairly accurate. As soon as the difference between them exceeds the threshold, P2138 sets. The second most common cause is wiring damage — a chafed wire or a pushed-back connector pin can cause one sensor's signal to drift differently from the other, which the PCM reads as correlation failure even though both sensors are technically healthy.
The driver experience is the familiar 'Reduced Engine Power' warning plus capped throttle response. Same limp mode as P2122, P2127, and P2135 — the PCM falls back to a safe state because it can't trust the pedal input.
Unlike P2135, P2138 has no DIY 'cheap test first' move. The pedal assembly can't be cleaned, can't be disassembled, and the sensors aren't separately serviceable on virtually any modern platform. The diagnostic split is purely between wiring and pedal-assembly replacement.
Common causes
- Worn or drifting pedal position sensors — internal wiper or Hall-effect element aging unevenly between D and E
- Damaged or chafed wiring at the pedal connector causing one signal to drift
- Pushed-back pin in the pedal connector affecting one sensor circuit
- Failed pedal assembly — sensors are not serviceable separately on most platforms
- Water intrusion at the pedal connector (less common, since pedals are inside the cabin)
- Recent under-dash work that disturbed the pedal harness
- Failed PCM input circuit for one of the pedal sensors (rare)
- Recent pedal assembly replacement without proper relearn
Symptoms
- Check Engine Light on
- 'Reduced Engine Power' warning on the dash
- Limp mode — throttle response capped at a fraction of normal
- Engine starts and idles normally
- Pedal feels mechanically normal but engine response is muted or delayed
- Sluggish acceleration that doesn't match pedal input
- May feel like the pedal has 'dead spots' where pressing harder doesn't produce more throttle
Diagnostic steps
- 1.Pull all codes. P2138 alone is the simple case. P2138 + P2122 or P2127 confirms that one pedal sensor is hard-failed (the partner low-input code) AND the correlation between them doesn't work.
- 2.Locate the pedal assembly under the dash and inspect the harness routing for damage, pinch points, or items stored under the front seat that could have damaged the wires.
- 3.Use a scan tool with live data capability. Watch both pedal sensor readings simultaneously as you press the pedal slowly from rest to full press. On a healthy pedal, both signals climb together with a consistent ratio between them. Disagreement, jumps, or one signal leading or lagging confirms a real correlation problem.
- 4.If one sensor is obviously failing (sticking, dropping out, non-linear response) and the other is smooth, the pedal assembly is the failure point.
- 5.If both sensors look healthy on live data but the code keeps setting, look for intermittent wiring damage — flex test the harness while watching scan tool readings.
- 6.Disconnect the pedal connector and check for pushed-back pins, water intrusion, or partial-release of the locking tab.
- 7.If wiring tests good and the pedal sensors don't track together on live data, replace the pedal assembly.
- 8.After any replacement, perform the platform-specific pedal relearn procedure.
Repair cost
$100 – $500
Low end is wiring repair when the diagnosis turns up a pinched wire or pushed-back pin — under $150 with diagnostic time included. Mid-range $200-350 is accelerator pedal assembly replacement on mainstream platforms — the part itself is $100-300 and labor is 30-60 minutes. Upper end is $400-500 for luxury platform pedal assemblies. Unlike P2135, there's no cheap 'cleaning' option here because the pedal assembly is sealed.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with accelerator pedal position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.