OBD-II trouble code
P2128: Throttle/Pedal Position Sensor 'E' Circuit High Input
The 'E' accelerator pedal position sensor is reading too high — a signal voltage above its expected window. As the high-input mirror of P2127, and the companion to the 'D'-channel code P2123, it usually traces to a short to voltage, a connector or wiring fault, or a failed pedal sensor. Drive-by-wire systems treat pedal signals as safety-critical, so reduced-power limp mode is common until it's fixed.
Quick facts
- System
- Powertrain
- Category
- Throttle / Idle
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $450
- DIY difficulty
- Intermediate DIY
Browse every code in P2100–P219A, or start from the full code library.
What does P2128 mean?
Electronic throttle (drive-by-wire) systems replace the throttle cable with redundant accelerator pedal position sensors. The pedal houses more than one sensor channel — commonly designated 'D' and 'E' — that produce different but correlated signals, letting the PCM cross-check them to catch a fault and then open the electronic throttle accordingly. P2128 sets when the 'E' channel's signal voltage stays above the expected range — the circuit-high condition, mirroring P2127 (circuit low) and paralleling P2123 on the 'D' channel. Because the pedal signal directly commands engine power, the PCM treats an out-of-range reading on either channel as serious.
The causes are electrical and identical in character to the other pedal-circuit faults, but it is worth knowing which of them produces a high reading by physics rather than by bad luck — because that is the one to check first and it takes two minutes. The sensor is a divider sitting between its reference voltage and its ground. Lose the ground and the bottom of that divider floats up toward the reference, so the signal reads high with nothing shorted to power anywhere in the car. An open in the signal wire itself commonly reads high too, depending on how the PCM biases that input. A genuine short to a voltage source — a chafed harness against a powered circuit — gives the same result but takes far longer to find, which is why it is not where to start. A corroded connector, or a failed sensor whose element has gone open internally, round out the list. Since the sensors are built into the pedal assembly, a failed 'E' sensor usually means replacing the pedal module. The PCM constantly compares the D and E signals; when 'E' goes out of range, the pair can no longer be trusted, so it falls back to a safe, reduced-power strategy.
For the driver, P2128 brings the same picture as its 'D'-channel sibling: a check engine light, reduced engine power or limp mode, sluggish or limited acceleration, and possible idle or throttle-response irregularities. The car is usually driveable enough to reach safety or a shop, but the power limitation is intentional. Diagnosis reads both pedal sensor signals, checks the 'E' circuit for a short to voltage, inspects the connector and reference/ground, and replaces the pedal sensor assembly if the circuit is good but the sensor reads high.
Common causes
- Open or high-resistance sensor ground, letting the signal float up toward the reference voltage
- Open 'E' signal wire between pedal and PCM
- Corroded or damaged pedal sensor connector
- Failed accelerator pedal position sensor with an internally open element
- Short to a voltage source in the 'E' signal wire — a chafed harness against a powered circuit
- Damage after pedal or harness service
Symptoms
- Check engine light with P2128 stored
- Reduced engine power or limp / failsafe mode
- Sluggish or limited acceleration
- Throttle that feels unresponsive
- Idle or revving irregularities
- Possible companion pedal-position codes such as P2123
Diagnostic steps
- 1.Read both pedal position sensor signals in live data and confirm the 'E' channel reads high or out of range.
- 2.Check the 'E' circuit's ground first — continuity and resistance from the sensor's ground pin to chassis ground. This is the cheapest test on the list and it is a complete explanation on its own: without a good ground the sensor's output floats high no matter how healthy the sensor is.
- 3.Inspect the pedal sensor connector for corrosion, damage, looseness and backed-out pins, and confirm the reference voltage is present and near its nominal value.
- 4.Check the 'E' signal wire for continuity back to the PCM. An open there will often read high as well, and it is quicker to prove than a short.
- 5.Only then go looking for a short to voltage, inspecting the harness run where it could chafe against a powered circuit. It produces the same reading as the faults above but costs far more time to locate.
- 6.Replace the pedal position sensor assembly if the circuit, reference, and ground are good but the sensor still reads high.
Repair cost
$150 – $450
Because the accelerator pedal position sensor is usually integrated into the pedal assembly, replacement runs roughly $150-$400 with labor depending on the vehicle. A wiring or connector repair can be less but takes diagnostic time to locate a short to voltage. As a safety-critical system, confirm the circuit and both sensor signals before replacing the pedal module.
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.