P2125
Accelerator Pedal Position (APP) Sensor 2 CircuitP2125 is a generic OBD-II powertrain diagnostic trouble code: Accelerator Pedal Position (APP) Sensor 2 Circuit. 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 P2125 means
P2125 is a generic OBD-II powertrain code defined as "Throttle/Pedal Position Sensor/Switch 'E' Circuit Malfunction." The broad 'malfunction' descriptor (as opposed to 'high' or 'low') means the PCM has detected that the E-circuit signal is outside its expected operating range or is behaving implausibly — this can include signals that are stuck, erratic, out of correlation with adjacent redundant circuits, or showing an open/short condition. Circuit E is typically one of the two redundant accelerator pedal position channels (often the second channel in a D/E pair), or on some platforms a secondary throttle position signal.
Modern electronic throttle control systems compare the outputs of two or more sensors simultaneously. If the E-circuit reading does not track logically with the D or F circuit when the pedal is pressed or released, the PCM flags a rationality fault even if the raw voltage appears within range. This cross-correlation test makes P2125 more sensitive than a simple range check, meaning intermittent faults — such as a sticking return spring causing a delayed signal change — can set this code.
A stored P2125 causes the PCM to restrict or disable throttle response (limp mode or forced idle) as a safety precaution against uncontrolled acceleration. The code will not clear itself during normal driving; the fault must be diagnosed and repaired, after which a throttle relearn is typically required.
Common causes
Most-frequently reported root causes when P2125 is logged.
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1
Open circuit or high-resistance connection in the APP/TPS E-circuit signal wire or reference voltage supply.
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2
Short to ground on the E-circuit signal wire pulling voltage below the plausibility window.
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3
Faulty accelerator pedal position sensor producing an erratic or stuck E-channel output.
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4
Sticking accelerator pedal return spring causing delayed or non-linear signal changes that fail rationality checks.
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5
Corroded or water-intruded connector at the pedal assembly, causing intermittent signal loss.
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6
E-circuit reference voltage (typically 5 V) lost due to a shared reference line fault affecting multiple sensors.
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7
PCM internal fault causing misinterpretation of the E-circuit (diagnose last after all external checks pass).
Symptoms drivers notice
How to diagnose P2125
A typical diagnostic flow when this code is present.
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1
Retrieve all stored DTCs with a scan tool; note any companion codes that may indicate a shared reference-voltage or ground fault.
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2
Inspect the accelerator pedal assembly connector and wiring harness for corrosion, bent pins, and chafing against nearby components.
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3
With KOEO, monitor live E-circuit voltage on a scan tool while slowly depressing and releasing the pedal; the signal should change smoothly and track the D-circuit proportionally.
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4
Measure E-circuit reference voltage (typically 5 V) at the sensor connector; a low or absent reference indicates a wiring or PCM supply fault upstream.
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5
Perform a resistance check on the signal wire from pedal connector to PCM pin; an open circuit confirms a wiring fault.
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6
If wiring is intact, substitute the pedal assembly with a known-good unit and re-test.
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7
After repair, clear codes and perform the manufacturer throttle relearn procedure before road-testing.
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 makes P2125 different from P2123 or P2128?
P2123 and P2128 specify a high-voltage condition on the D or E circuit respectively, meaning the voltage exceeded the upper calibration limit. P2125 is a broader 'malfunction' flag that covers any implausible E-circuit behaviour — including out-of-range voltage, an erratic signal, or a rationality failure when compared against a redundant sensor channel.
Can a sticking gas pedal cause P2125?
Yes. If the accelerator pedal return spring is stiff or binding, the sensor signal may lag or move non-linearly compared to actual pedal travel. The PCM's cross-correlation logic can interpret this lag as a sensor malfunction and set P2125.
Why are there so many redundant throttle sensor circuits (A through F)?
Electronic throttle control systems use multiple independent sensor elements to provide fail-safe redundancy. The PCM continuously compares these signals; if any one diverges from the expected relationship to the others, it flags a fault and limits throttle authority to prevent unintended acceleration.
Will replacing the accelerator pedal assembly always fix P2125?
Not always. If the root cause is an open or corroded signal wire, a faulty 5 V reference supply, or a damaged PCM pin, replacing the pedal will not resolve the code. Thorough wiring and reference-voltage checks must be completed before part replacement.
Disabling P2125 in software
RaceTune can permanently disable P2125 — 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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