P2138 Code: Accelerator Pedal Position Sensor D/E Voltage Correlation
The two sensors in the gas pedal report different pedal positions, so the PCM limits throttle response.
At a glance
Severity: Moderate
- Meaning
- Accelerator Pedal Position Sensor D/E Voltage Correlation
- System
- Speed & Idle Control · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$450
- DIY difficulty
- Easy
A drive-by-wire gas pedal contains two independent position sensors, D and E, each with its own reference, ground and signal wire. They are built to give different voltages on purpose so a single short can't make them agree by accident. Common pairings are a half-slope design, where E reads about half of D (for example around 1.0 V and 0.5 V at rest, rising to roughly 4.5 V and 2.2 V at the floor), an offset design where E sits a fixed amount above D, or a mirror-image design. The PCM converts both to percent of pedal travel, and when they differ by more than a few percent it sets P2138. Worn sensor tracks in the pedal module are the leading cause, followed by the pedal connector, a shared reference or ground fault, and plug-in throttle response controllers.
Can I keep driving? You can usually drive carefully, but acceleration will be slow or capped and the car may drop to idle when you touch the brake. Avoid merging onto highways or passing until it's fixed.
How to read P2138
- P Powertrain
- 2 Generic (SAE)
- 1 Fuel & air metering
- 38 Specific fault
Symptoms
- Check engine light with Reduced Engine Power, a wrench light or a similar message
- Delayed, soft response to the gas pedal and a low top speed
- Engine returns to idle whenever the brake pedal is pressed
- Fault appears over bumps or at light pedal and clears after a restart
- Cruise control disabled while the code is active
- Pedal D and E percentages in live data that don't match at the same pedal position
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Worn sensor tracks inside the accelerator pedal module
- Loose, corroded or spread terminals in the pedal connector
- Shared 5-volt reference or sensor ground fault affecting one track
- Plug-in throttle response controller or pedal booster between pedal and harness
- Wrong or used replacement pedal with a different sensor characteristic
- Harness pinched behind the dash or a PCM input fault
Diagnosis step by step
Record both pedal signals at rest and at the floor
Key on, engine off, read pedal D and E in volts. Work out their relationship at rest and fully pressed: on a half-slope pedal E should stay close to half of D, on an offset pedal the gap should stay constant. A relationship that holds at rest but breaks partway down points to wear.
Tools: OBD-II scanner
Graph a slow pedal sweep
Press the pedal slowly to the floor and back over about ten seconds while graphing both signals. Look for a notch, dropout or step on one trace, most often in the first third of travel where the pedal spends its life. Also push the pedal sideways lightly; if a reading moves, the pivot is worn.
Tools: OBD-II scanner
Remove add-ons and inspect the connector
Unplug any throttle response controller and reconnect the original harness directly to the pedal. Check the connector on the pedal module for green corrosion, loose terminals or a broken lock, and feel the carpet for dampness from a leaking cowl or wet shoes.
Tools: Flashlight, Screwdriver
Check references and grounds at the pedal
Most pedal connectors carry six wires: two 5-volt references, two grounds, two signals. Back-probe with the key on; both references should read 4.9–5.1 V and both grounds should be within about 0.1 V of battery negative. A low reference on one track only means a wiring or shared-sensor fault, not the pedal.
Tools: Multimeter
Replace the pedal module with the correct part
The sensors aren't sold separately; the whole pedal assembly is replaced, usually with two or three nuts and one connector. Match the part to the vehicle identification number, because pedals that look alike can use different sensor curves.
Tools: Screwdriver, OBD-II scanner
Clear, relearn if required, and verify
Clear the codes, perform a pedal learn if your make requires one, and repeat the graphed sweep. Both traces should move smoothly together. Road test over rough pavement to confirm the fault doesn't return.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Remove aftermarket throttle controller and reconnect original harness | Yes | $0–$50 |
| Clean or repin the pedal connector | Yes | $60–$180 |
| Replace accelerator pedal module | Yes | $150–$450 |
| Repair pedal wiring behind the dash | No | $150–$400 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Chevrolet
On GM trucks and SUVs, P2138 with a Reduced Engine Power message is a familiar complaint. A new accelerator pedal assembly is the most common fix, but check the pedal connector and the shared 5-volt references first.
Jeep
P2138 shows up regularly on Jeep models with electronic throttle. The pedal module and its connector are the usual findings; water in the driver footwell makes the connector more likely to corrode.
Ford
On Fords, P2138 often lights the orange wrench symbol along with or instead of the check engine light, and the vehicle limits power. The pedal assembly is the typical repair once wiring checks out.
Field data
| Chevrolet | 116 | ||
|---|---|---|---|
| Subaru | 85 | Outback, Legacy, Forester | |
| GMC | 10 | Yukon Xl, Acadia, Sierra 1500 | |
| Nissan | 5 | Versa Hatchback, Altima, Leaf | |
| Jeep | 4 | Renegade, Patriot, Wrangler | |
| Kia | 4 | Sorento, Sedona | |
| Honda | 3 | Accord, Cr-V, Element | |
| Dodge | 2 | Grand Caravan, Journey |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
With P2138 stored the check engine light is on and an OBD-II emissions inspection will fail. The code usually clears quickly after a correct repair, but the readiness monitors still need a few drives.
Frequently asked questions
Can a floor mat cause P2138?
Not directly. A mat that holds the pedal down moves both sensors together, so they still agree. It can, however, cause unwanted revving or a brake-throttle override, so remove stacked or loose mats anyway while diagnosing.
How do I tell whether the pedal or the wiring is at fault?
If the graph shows a glitch at the same pedal angle every time and your hands are off the wiring, the pedal is worn. If the glitch follows wiggling the connector or harness, or one reference voltage is low, the wiring or a shared sensor is to blame.
Does a new gas pedal need programming?
Many vehicles accept a new pedal after the codes are cleared and the key is cycled. Some makes want a closed-pedal learn or a scan tool routine, so check the procedure for your vehicle.
Why does the code come and go?
A worn track usually fails only at one small spot, so the fault sets only when you hold the pedal there. That's why a slow graphed sweep finds it far more reliably than a quick look at the numbers.