P2122
Accelerator Pedal Position (APP) Sensor 1 Circuit Low VoltageP2122 is a generic OBD-II powertrain diagnostic trouble code: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P2122 means
P2122 is triggered when the PCM measures a voltage on throttle or accelerator pedal position sensor circuit D that falls below the manufacturer's defined minimum threshold — typically below approximately 0.17–0.20 V, depending on the vehicle. The D circuit is one of several redundant sensor circuits used in drive-by-wire systems to report accelerator pedal position or throttle plate angle to the PCM. A signal that drops this low usually indicates a short to ground, an open circuit pulling the line low, high-resistance corrosion, or a failed sensor element.
In practice, the most common cause is a problem at the connector of the accelerator pedal assembly itself. Salt, moisture, and engine-bay contamination corrode terminal surfaces and reduce contact pressure, adding resistance that drops the circuit voltage below the threshold. Similarly, chafed wiring that rubs against chassis metal can create intermittent or permanent shorts to ground. Cold weather accelerates both problems, as metal contraction can open marginal connections or increase existing resistance.
Because a low-voltage signal on the D circuit could be interpreted as the driver requesting zero throttle, the PCM prioritises safety and activates limp mode, typically capping engine speed at around 2,000–2,500 rpm and limiting available torque. The vehicle may also exhibit intermittent stalling or a dead-pedal sensation where pressing the accelerator produces no response. In severe cases the engine may not start.
Diagnosis begins by verifying the fault with live scan-tool data and checking the reference voltage at the pedal connector (should be close to 5 V). A voltage-drop test on the signal and ground wires isolates resistive connections. If wiring and connectors are sound, the accelerator pedal position sensor assembly is the next replacement candidate.
Common causes
Most-frequently reported root causes when P2122 is logged.
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1
Corroded or loose connector terminals at the accelerator pedal assembly
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2
Short to ground in the sensor D signal wire
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3
Open circuit in the signal wire creating a low-pull condition
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4
High-resistance chafed wiring between pedal and PCM
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5
Failed or worn accelerator pedal position sensor element
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6
Faulty 5 V reference supply from the PCM to the sensor
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7
Damaged sensor ground circuit increasing voltage drop
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8
Water or moisture intrusion into the pedal assembly connector
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9
Aftermarket wiring additions introducing unintended resistance or grounding
Symptoms drivers notice
How to diagnose P2122
A typical diagnostic flow when this code is present.
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1
Confirm P2122 with a scan tool and capture freeze-frame data; note battery voltage and pedal position readings at the time of the fault
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2
Monitor live sensor D voltage while slowly sweeping the pedal from rest to full throttle — a healthy signal sweeps smoothly from approximately 0.5 V to 4.5 V
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3
Check the 5 V reference voltage at the pedal assembly connector with a multimeter; a low or absent reference points to a PCM supply fault
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4
Perform a voltage-drop test on the sensor ground circuit; a drop above 0.1 V indicates a faulty ground path
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5
Perform a wiggle test on the pedal harness and connector while watching live data to detect intermittent faults
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6
Measure signal wire continuity and resistance from the pedal connector to the PCM connector; resistance above 1 Ω warrants repair
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7
Replace the accelerator pedal position sensor assembly if wiring and reference supply tests pass
Related powertrain codes
- B0001 — PCM Discrete Input Speed Signal Error
- B0004 — PCM Discrete Input Speed Signal Not Present
- C0359 — Four Wheel Drive Low Range (4LO) Discrete Output Circuit
- C0362 — 4LO Discrete Output Circuit High
- P2000 — NOx Adsorber Efficiency Below Threshold Bank 1
- P2001 — NOx Adsorber Efficiency Below Threshold Bank 2
Frequently asked questions
What voltage should the D circuit read at idle?
On most vehicles, the resting (pedal released) voltage for the D circuit is approximately 0.5–0.8 V, rising to around 4.0–4.5 V at wide-open throttle.
Is the accelerator pedal module a common failure item?
Yes. The pedal position sensor is a wear item subject to contamination and connector corrosion.
Can P2122 be caused by a dead battery or low charging voltage?
Indirectly, yes. Low system voltage reduces the 5 V reference supply, which in turn lowers the sensor output.
What other codes appear alongside P2122?
P2127 (sensor E circuit low), P2121 (sensor D range/performance), P2123 (sensor D circuit high), and P2135 (TPS A/B correlation) are common companions.
Does replacing the sensor require recalibration?
Most vehicles require an idle or throttle relearn after replacing the pedal sensor assembly.
Disabling P2122 in software
RaceTune can permanently disable P2122 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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