P2138 Code: Accelerator Pedal Position Sensor 1-2 Correlation (Chevrolet Guide)

P2138 on a Chevrolet is "Accelerator Pedal Position (APP) Sensor 1-2 Correlation." The two sensors inside your gas pedal disagree about where the pedal is, so the engine computer limits power and you get the "Engine Power is Reduced" message. GM has a fleet-wide bulletin on this code for every 2018-and-earlier GM car and light truck, and its first finding is not the pedal at all — it is water getting into a wiring connector behind the instrument panel. GM also had special coverages on the pedal itself for the 2016–2018 Malibu and the 2009–2011 Impala.

What Does P2138 Mean?

Your accelerator pedal is not connected to the engine by a cable. It is a sensor assembly, and the engine computer reads it to decide how far to open the throttle.

Because a wrong pedal reading could open the throttle when nobody asked, the pedal contains two separate position sensors, each with its own 5-volt reference, low reference and signal wire back to the ECM. They are deliberately scaled differently — in one GM service example, sensor 1 idles near 1 volt and sensor 2 near half a volt — but both rise together as you press the pedal.

GM's bulletin describes the setting condition: P2138 sets when there is a voltage difference between APP sensor 1 and APP sensor 2 that exceeds a predetermined value for more than a calibrated period of time. In GM service information for a related platform, that threshold is a disagreement of more than about 10%. It is a Type A code — one failure turns on the check engine light — and the ECM puts the throttle control into reduced power.

P2138 Is the Pedal, Not the Throttle

GM builds the same two-sensor redundancy into two places, and they set different codes:

• P2138 — the two sensors in the accelerator pedal disagree.
• P2135 — the two sensors in the throttle body disagree.

Both produce "Engine Power is Reduced," which is why they get mixed up. GM's well-known throttle body coverages — Special Coverage 14582 and 11273A, which covered Silverado, Tahoe, Malibu, Impala and many others — use P2135, P0121 and P0221 as entry codes. P2138 is not one of them. A throttle body sold for a P2138 is the wrong part.

The one exception: the pedal and throttle sensors can share 5-volt reference circuits. A shorted sensor elsewhere can drag down a shared reference, and that shows up as its own 5-volt reference code. See our P0641/P0651 guide.

GM's Fleet-Wide Bulletin: Water in the Connector

GM bulletin 07-06-04-019F (November 2017) is titled "Intermittent MIL Illuminated, DTC P2138 with Reduced Engine Power (Repair IP to Body Harness Connector)." It applies to 2018 and prior GM passenger cars and light-duty trucks — Silverado, Tahoe and the rest of the lineup included.

The pedal signals reach the ECM through the instrument panel-to-body harness connector, usually near the left kick panel or inside the dash. GM's cause is water entering that connector, from leaking A-pillar seals, clogged sunroof drains or windshield and cowl leaks.

GM's steps:

1. Check for aftermarket equipment spliced into the pedal signal, low reference, or any ECM 5-volt or low-reference circuit. GM states plainly that aftermarket equipment can generate P2138.
2. If any 5-volt reference codes are set, diagnose those first.
3. Find and fix the water leak, clean or repair the connector terminals, and verify the repair.

No parts are listed — the labor operations are for resealing. If your P2138 is intermittent, look for water staining at the driver's kick panel before anything else.

GM documented a related harness problem on the 2010–2015 Equinox in bulletin 16-NA-012: the pedal harness was mis-routed and under tension, damaging its connector. That bulletin describes reduced power and DTCs without naming P2138 specifically, so we list it as related rather than as a P2138 bulletin.

Special Coverages on the Pedal

Special Coverage N182188250 (August 2019) — 2016–2018 Chevrolet Malibu, plus 2017–2018 Buick LaCrosse and 2018 Regal. GM describes a loss of continuity within the accelerator pedal position sensor circuit, with P2138 named. Coverage is 10 years or 150,000 miles. The repair is a new pedal assembly as needed (parts 84478055 or 84478060, chosen by VIN). On the 1.5L Malibu only, GM adds a harness check: the engine harness can be chafed by the heater inlet hose clamp. The fix is to rotate the clamp for at least 3/4 inch (19 mm) of clearance, or replace the hose and clamps, and wrap the harness.

For a 2016–2018 Malibu, that coverage window is still open on many vehicles. A dealer VIN check is free.

Special Coverage 14636 (April 2015) — 2009–2011 Chevrolet Impala and 2009 LaCrosse/Allure. Cause: a broken solder connection inside the pedal sensor. Coverage was 10 years or 120,000 miles, which has now passed for practical purposes. The repair was pedal assembly 22742315.

GM also issued emission recall 14176B on the 2014 Cadillac ATS for improperly crimped pedal sensor terminals that set P2138 — not a Chevrolet, but another example of the same failure being in the wiring rather than the pedal.

Reduced Power and Why It Matters

Reduced power is the right response when the computer cannot trust the pedal: acting on a wrong reading could mean unintended acceleration. But it arrives without warning, and limited acceleration in the middle of a merge or a pass is a real hazard. On some GM vehicles, P2138 also disables traction control and StabiliTrak, which GM documented on the ATS recall.

So this is not one to commute on. The vehicle will move, but reduced power is meant to get you somewhere safe. Cycling the ignition may restore power temporarily; that is not a repair.

Symptoms of P2138

• "Engine Power is Reduced" message and limited acceleration
• Check engine light on
• Intermittent loss of throttle response, sometimes after rain or a car wash
• "Service Traction Control" or "Service StabiliTrak" messages on some models
• Power returning after the engine is restarted, then the fault coming back
• Companion codes P2122/P2123 or P2127/P2128 (individual pedal sensor circuits)

Causes and How to Confirm Each

How Is P2138 Diagnosed?

1. Confirm it is P2138, not P2135. Pedal versus throttle decides the part.
2. Record every code. Diagnose any 5-volt reference codes first.
3. Check the VIN for N182188250 (2016–2018 Malibu) and any other open coverage.
4. Look for aftermarket equipment tied into the pedal or reference circuits.
5. Inspect the left kick panel and IP-to-body connector for water; find the leak source.
6. Watch APP 1 and APP 2 on a scan tool through slow and fast pedal sweeps, wiggling the harness.
7. Test the reference, low reference and signal circuits per the wiring diagram.
8. Replace the pedal assembly only when the fault follows the pedal. Order it by VIN.
9. Clear the code and road test, including after rain or a wash if the fault was intermittent.

Parts and Cost

GM Documents That Name P2138

Have a dealer check your VIN against current coverages rather than relying on any article, including this one.

What Other P2138 Pages Get Wrong

• Replacing the throttle body. P2138 is the pedal. GM's throttle body coverages use P2135, not P2138.
• Going straight to the pedal. GM's fleet-wide bulletin starts with water in a connector behind the dash.
• Ignoring aftermarket accessories. GM says aftermarket equipment can generate P2138.
• "Just clear it." It is a reduced-power code that can return in traffic.
• Missing the Malibu coverage. 2016–2018 Malibu pedal failures are covered for 10 years or 150,000 miles.
• Skipping the 5-volt codes. GM says diagnose those first; a shared reference fault can mimic a bad pedal.

Frequently Asked Questions

Can I drive with P2138?

Only as far as you need to. Reduced power can come on without warning and limit acceleration in traffic. Restarting may restore power temporarily, but the fault will return.

Is P2138 the gas pedal or the throttle body?

The gas pedal. P2138 means the two sensors inside the accelerator pedal assembly disagree. The throttle body version is P2135.

Is my 2016–2018 Malibu pedal covered?

GM Special Coverage N182188250 covers pedal sensor continuity faults with P2138 on 2016–2018 Malibu for 10 years or 150,000 miles from the in-service date. A dealer VIN check confirms it.

Why does my P2138 come and go with the weather?

GM's 07-06-04-019F describes water entering the instrument panel-to-body harness connector from A-pillar, sunroof drain or windshield leaks. A fault that shows up after rain or a wash fits that pattern exactly.

Can a remote starter cause P2138?

GM's bulletin says aftermarket equipment connected to the pedal signal or the ECM's reference circuits can generate P2138. If something was installed around the time the code started, check its wiring.

What should I check after replacing the pedal?

Follow the service procedure for your vehicle, then watch APP sensor 1 and 2 on a scan tool through a full pedal sweep. Both should rise smoothly, and the agree/disagree status should read Agree from closed to wide open before you drive it.