P2128
Accelerator Position Sensor 2 (G185): Signal too HighP2128 is a generic OBD-II powertrain diagnostic trouble code: Accelerator Position Sensor 2 (G185): Signal too High. 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 P2128 means
P2128 is a generic OBD-II powertrain code defined as "Throttle/Pedal Position Sensor/Switch 'E' Circuit High Input." It is the high-side companion to P2127 (E circuit low) and is triggered when the PCM measures a voltage on the E circuit that exceeds the calibrated upper threshold — typically above approximately 4.7 V on a 0–5 V sensor reference system. The E designator most commonly refers to the second channel of the accelerator pedal position (APP) sensor in a D/E redundant pair, though on some platforms it represents a secondary throttle position signal on the throttle body.
A high-circuit condition is almost always caused by a short to a voltage source — either the 5 V sensor reference rail, the 12 V battery supply leaking into the signal wire, or an internal sensor element failure with the wiper contact permanently shorted to the supply. Because drive-by-wire systems require both redundant sensor channels to agree within a narrow tolerance, a stuck-high E-circuit is immediately detected and treated as a safety hazard by the PCM. Some manufacturers also require both APP sensor elements to be replaced as an assembly, since the channels share a substrate and their characteristics are factory-matched.
As with all ETC redundant-channel faults, the PCM enters limp mode or forced-idle upon detection and illuminates the MIL. The vehicle will not resume normal throttle operation until the fault is repaired and — on most platforms — a throttle angle relearn cycle is performed via scan tool.
Common causes
Most-frequently reported root causes when P2128 is logged.
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1
Short to voltage (5 V reference or 12 V supply) on the E-circuit signal wire.
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2
Internal APP or TPS sensor failure with the E-channel wiper element shorted to the supply internally.
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3
Damaged wiring insulation causing the E-signal wire to contact a power feed wire in the harness.
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4
Water intrusion into the pedal assembly or throttle body connector shorting signal to supply.
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5
Corroded or damaged connector terminals creating unintended continuity to a voltage source.
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6
Throttle body contamination (carbon buildup) holding the plate open, producing a sustained high E-circuit reading.
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7
PCM supply-reference fault sending excess voltage down the reference line shared with the E circuit.
Symptoms drivers notice
How to diagnose P2128
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and confirm P2128 is stored; check for companion TPS/APP codes that may point to a shared reference fault.
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2
Inspect the pedal assembly and throttle body wiring harness for visible chafing, melted insulation, or connector damage.
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3
With KOEO and the pedal assembly connector unplugged, measure the E-circuit signal wire voltage at the harness side; voltage above ~0.1 V indicates a short to power in the wiring.
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4
If the harness measures correctly, reconnect the sensor and perform a live data sweep — slowly depress the pedal and watch the E-circuit voltage; a sudden jump to maximum at any pedal position suggests an internal sensor fault.
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5
Measure the 5 V reference voltage at the sensor connector; if it reads above ~5.2 V, suspect a PCM reference supply fault.
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6
Replace the pedal assembly (or throttle body TPS if the E circuit maps there on this platform) and retest.
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7
Clear codes, perform the throttle relearn procedure, and verify normal operation with a complete drive cycle.
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
Is P2128 the same fault as P2123 just on a different circuit?
They are mechanically similar — both indicate a redundant throttle/pedal circuit voltage above calibrated limits — but they cover different sensor channels. P2123 is the D circuit and P2128 is the E circuit. On most platforms the D and E circuits are the two channels of the accelerator pedal assembly, so the same component is involved but a different internal element.
Can I clear P2128 and keep driving?
Clearing the code temporarily exits limp mode, but if the underlying fault persists the code will return, often within a single key cycle. Continuing to operate the vehicle without repair risks being stranded and does not address the safety concern that triggered the limp mode strategy.
Why do some manufacturers require replacing the entire throttle body when P2128 is set?
On many drive-by-wire systems the TPS elements are integrated into the throttle body motor housing and are factory-calibrated as a matched set. The PCM performs a relearn against both channels simultaneously; a replacement single element may not match the remaining original channel closely enough to pass the rationality check.
Could P2128 be triggered by a software issue rather than a hardware fault?
Occasionally, a corrupted PCM calibration table or a module communication error can generate a false high-voltage interpretation. However, this is rare; always rule out wiring, connector, and sensor faults first. A PCM reflash or replacement should only be considered after all hardware paths have been eliminated.
Disabling P2128 in software
RaceTune can permanently disable P2128 — 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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