P2128 Code: Accelerator Pedal Position Sensor E Circuit High
The second gas pedal sensor reads above its allowed maximum, so the pedal position can't be cross-checked.
At a glance
Severity: Moderate
- Meaning
- Accelerator Pedal Position Sensor E Circuit High
- System
- Speed & Idle Control · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$450
- DIY difficulty
- Moderate
P2128 means pedal sensor E rose above the PCM's upper limit, typically close to the 5-volt reference. How the reading behaves points to the cause. If E sits near 5 V and barely moves when you press the pedal, the sensor has most likely lost its ground or its signal is touching a reference wire. If E still follows the pedal but is shifted too high across the whole travel, look at extra resistance in the ground path or at a replacement pedal whose E curve doesn't match what the PCM expects; pedals that look identical can differ inside. On mirror-image designs E is highest at rest, so a problem there appears with the pedal released. Because the sensor grounds for pedal and other sensors often meet at a common splice, a loose splice can set several high codes at once. With E unusable, the PCM limits throttle opening.
Can I keep driving? Usually drivable at reduced power. Get the fault diagnosed soon, especially if other sensor codes appeared at the same time, because a shared ground problem can spread to more sensors.
How to read P2128
- P Powertrain
- 2 Generic (SAE)
- 1 Fuel & air metering
- 28 Specific fault
Symptoms
- Check engine light with reduced power or a limp-mode message
- Pedal E stuck near 4.8–5 V and hardly changing with pedal movement
- Or pedal E moving normally but reading too high at every position
- Code appeared right after the pedal assembly was replaced
- Other sensor high codes stored at the same time
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Open or high-resistance E ground, including a shared sensor-ground splice
- Pedal sensor E failed with its output high
- Replacement pedal with the wrong sensor curve for the vehicle
- E signal shorted to a reference wire through water, pin damage or a pinched harness
- Aftermarket pedal controller or accessory spliced into the pedal wiring
- PCM input fault
Diagnosis step by step
Characterize the E reading
Key on, engine off, read E at rest and at the floor and compare with your vehicle's specification. Stuck near 5 V points to a lost ground or a short to reference; a correct shape but offset upward points to ground resistance or a mismatched pedal.
Tools: OBD-II scanner
Check the pedal part if it was replaced
If the code started after a pedal replacement, compare the part number on the new pedal with the original or have it checked by VIN. Used or generic pedals are a common source of an E curve the PCM rejects.
Tools: Flashlight
Compare the two sensor grounds
With the pedal plugged in and key on, back-probe the D ground and E ground pins and measure between them. They should be within a few hundredths of a volt of each other. A clear difference means E's ground path has resistance or is open.
Tools: Multimeter
Follow the ground to its splice
Use the wiring diagram to find where E's ground joins other sensor grounds or the PCM ground. If other sensors on that splice also show high codes, inspect and repair the splice before replacing anything.
Tools: Multimeter, Flashlight
Check for a pin-to-pin short
Disconnect the battery, unplug the pedal and PCM, and check for continuity between E's signal wire and every reference wire in the harness. Any continuity means damaged insulation or water bridging terminals.
Tools: Multimeter
Replace the pedal if the circuit is sound
If the ground is good, there's no short and the correct part is fitted, the sensor has failed. Replace the pedal module, clear the codes and confirm E sits at its specified rest value and keeps a constant relationship with D.
Tools: Screwdriver, 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 |
|---|---|---|
| Repair sensor-ground splice or ground wire | No | $100–$320 |
| Replace accelerator pedal module with the correct part | Yes | $150–$450 |
| Remove aftermarket pedal device and restore wiring | Yes | $0–$150 |
| Repair harness short or water-damaged connector | No | $120–$380 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Chevrolet | 2 | Avalanche |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
P2128 turns on the check engine light, so the vehicle fails an OBD-II emissions inspection. If a shared ground splice was repaired, confirm all related sensor codes are gone too.
Frequently asked questions
I just put in a new pedal and now have P2128. Why?
The replacement may not match your vehicle. Pedals that fit the same mounting can use different sensor curves, and the PCM rejects an E signal outside the range it expects. Check the part number against your VIN.
Why do several sensors show high codes at once?
Sensor grounds are often joined at a common splice. If that splice corrodes or breaks, every sensor on it loses its ground and its signal floats up toward the reference voltage.
Is P2128 worse than P2127?
Not in how the car drives; both leave the PCM without its cross-check sensor and it limits power either way. The difference is in the cause: high usually means lost ground or a short to voltage, low usually means lost reference or a short to ground.
Can a pedal tuning box cause P2128?
Yes. These devices rescale the pedal signals, and a fault or a loose plug can send an E signal above the limit. Reconnect the factory wiring first when diagnosing.