OBD-II trouble code
P2122: Throttle/Pedal Position Sensor 'D' Circuit Low Input
One of the two sensors inside the accelerator pedal assembly is reporting near-zero voltage no matter where the pedal is. Different from P0122 — this code is about the pedal side of the drive-by-wire system, not the throttle body.
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 P2122 mean?
On a modern drive-by-wire vehicle, the accelerator pedal isn't connected to the throttle by a cable. Instead, the pedal contains two independent position sensors (commonly labeled A/B or D/E depending on the platform) that report pedal position to the PCM. The PCM uses both sensors to confirm the driver's intent — if both agree, the PCM moves the electronic throttle plate to match. If they disagree, or if one sensor fails, the PCM falls back to a safety mode that limits power.
P2122 sets when the 'D' sensor inside the pedal assembly reports a signal voltage at or below the lower threshold (typically below 0.2-0.3V) regardless of where the pedal actually is. This is an electrical failure pattern — the sensor isn't drifting or wearing; the circuit is broken, shorted to ground, or the sensor element has failed internally. The PCM treats this as an untrustworthy pedal reading and goes into reduced-power mode.
The driver experience with P2122 is similar to other throttle-system failures: 'Reduced Engine Power' warning, throttle response capped at limp-mode levels, can't accelerate to highway speeds. The engine still starts and idles, but pressing the pedal doesn't produce the expected throttle opening. On most platforms, the second pedal sensor (E or B) is still working and is enough to keep the engine running, just with strict power limits.
The most common cause is wiring damage inside the pedal harness or at the pedal connector. Pedal assemblies live under the dash where they don't see weather or heat, so the failure isn't usually corrosion or thermal damage — it's more often a wire that got crushed by something stuffed under the seat, kicked loose by the driver's feet, or damaged during interior trim work. The second cause is internal sensor failure. The third is connector issues — pushed-back pins, partially-released locking tabs.
Common causes
- Damaged or pinched wiring in the pedal assembly harness
- Internal failure of the 'D' position sensor inside the pedal
- Pushed-back pin or damaged locking tab at the pedal connector
- Open or shorted-to-ground signal wire between the pedal and the PCM
- Open or shorted-to-ground 5V reference voltage to the pedal sensor
- Failed pedal assembly — sensors and electronics are integrated, not serviceable separately
- Recent interior or under-dash work that disturbed the pedal harness
- Failed PCM input circuit (rare)
Symptoms
- Check Engine Light on, often immediately at key-on
- 'Reduced Engine Power' warning on the dash
- Limp mode — throttle response is severely limited
- Engine starts and idles normally but won't respond fully to pedal input
- Pedal feels normal mechanically but the engine isn't accelerating
- May stall during driving if the second pedal sensor (E) also has issues
- Slower-than-normal idle drop when releasing the pedal
Diagnostic steps
- 1.Pull all codes. P2122 alone is one story. P2122 + P2127 means both pedal sensors are reading low (look at shared wiring, not the sensors individually). P2122 + P2138 means there's also a correlation issue between the two pedal sensors.
- 2.Locate the pedal assembly — under the dash where the accelerator pedal hinges. Pedal connector is usually a 6-pin connector on the top of the assembly.
- 3.Inspect the harness routing for visible damage, pinch points, or signs of items stored under the front seat.
- 4.Disconnect the pedal connector. With key on, measure voltage between the 'D' sensor signal pin and chassis ground (harness side). Should see between 0.5V and 4.5V depending on key-on state, NOT pegged at 0V.
- 5.Verify 5V reference and ground continuity at the connector — same tests as any TPS-style sensor.
- 6.Reconnect the pedal and watch live data on a scan tool. Press the pedal slowly through its full range. 'D' sensor should sweep smoothly from low voltage at rest to high voltage at full press. Stuck-low confirms the failure.
- 7.If wiring tests good and the sensor reads pegged-low when connected, the pedal assembly is the failure (sensors are not separately serviceable on most platforms).
- 8.After replacement, perform the pedal relearn procedure for your platform.
Repair cost
$100 – $500
Low end is a wiring repair if the cause is a pinched harness or pushed-back pin — under $150 with diagnostic time. Mid-range $200-350 is pedal assembly replacement on mainstream platforms. Upper end $400-500 covers luxury platform pedal assemblies or platforms where the pedal is integrated with brake and accelerator assemblies that require more disassembly. Most pedal assemblies are bolted in with 2-3 nuts and the job is straightforward once the diagnosis is confirmed.
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.