P0228

Throttle/Pedal Position Sensor/Switch C Circuit High Input

P0228 is a generic OBD-II powertrain diagnostic trouble code: Throttle/Pedal Position Sensor/Switch C Circuit High Input. It is logged by the engine control unit when the throttle monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0228
Group
Powertrain
System
Throttle
Severity
Critical (limp mode / no-start)
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What P0228 means

P0228 is a generic OBD-II code indicating that the PCM detected a signal voltage from the Throttle Position Sensor or Accelerator Pedal Position sensor channel "C" that exceeds the upper calibrated threshold — typically above approximately 4.5–4.8 volts when a wide-open-throttle reading near that value would be expected only at full pedal application. A persistent over-voltage signal at all throttle positions is interpreted by the PCM as a "stuck high" condition, which is equally dangerous as a stuck-low fault because it could be misread as a full-throttle command. This distinguishes P0228 from P0226, where the signal is in range but disagrees with the other channels.

The most common causes are a short to the reference voltage or battery voltage on the C-channel signal wire, an open ground circuit that forces the signal pin to float toward reference, or an internally failed sensor whose C-track wiper has shorted internally to the high side. On multi-channel APP sensors, the PCM compares all channels and will immediately flag the disagreement, engaging a forced-idle or reduced-power strategy to prevent an unintended high-throttle event.

Diagnosis should start with a signal voltage measurement at the C-channel pin with ignition on. A reading near or above 4.8 V at rest (closed throttle) confirms the high-input fault. The technician should then disconnect the sensor: if the voltage drops significantly, the sensor is the source of the high signal; if it remains high, a short to voltage in the harness is the cause. The PCM itself is rarely the source of this fault but should be evaluated after all external causes are eliminated.

Common causes

Most-frequently reported root causes when P0228 is logged.

  • 1
    Short circuit to the 5-volt reference supply or battery voltage on the C-channel signal wire.
  • 2
    Open sensor ground circuit causing the signal pin to float toward the reference voltage.
  • 3
    Internally failed TPS or APP sensor with the C-track wiper shorted to the high-side supply internally.
  • 4
    Corroded or damaged connector with a pin bridging the signal and reference terminals.
  • 5
    Chafed wiring where the C-channel signal wire contacts the reference or power wire.
  • 6
    Improperly installed aftermarket sensor with incompatible resistance characteristics.
  • 7
    PCM internal fault on the C-channel input pull-up circuit (rare).

Symptoms drivers notice

MIL illuminated with P0228 stored; electronic throttle control or traction control warning lights may also activate.
Immediate limp-home mode with severely restricted engine output — typically limited to approximately 20 mph.
Unresponsive or sluggish throttle; the PCM disregards the C-channel reading and defaults to a safe minimum throttle strategy.
Elevated fuel consumption as the PCM applies conservative fuel maps in the absence of reliable throttle data.
Possible hard starting if the high signal persists at key-on and the PCM interprets it as a sensor error before enabling normal start logic.

How to diagnose P0228

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all stored codes and freeze frame data; note whether companion P0223 (APP-A high) or P0225 codes are present, which may indicate a shared reference supply short.
  2. 2
    With ignition on and engine off at closed throttle, measure the C-channel signal voltage at the sensor connector — a reading near or above 4.8 V confirms the fault.
  3. 3
    Disconnect the sensor and recheck signal voltage at the harness side — if voltage drops toward zero, the sensor itself is shorted internally; if it remains high, there is a short to voltage in the harness.
  4. 4
    Inspect the wiring harness for chafing where the C-channel signal wire runs near the 5-volt reference or any ignition-voltage source.
  5. 5
    Check sensor ground integrity; measure resistance from sensor ground pin to chassis ground (should be near zero ohms).
  6. 6
    Inspect connector terminals for bridged or bent pins that could cause signal and reference terminals to contact.
  7. 7
    After repair, clear codes, perform a full throttle sweep with live data, and confirm C-channel voltage sweeps smoothly from approximately 0.5 V at idle to 4.5 V at WOT.

Related powertrain codes

Frequently asked questions

Why is a high-voltage signal on TPS channel C so dangerous?

The PCM interprets a persistently high C-channel voltage as a near-full-throttle command. On a drive-by-wire system, if the PCM acted on this signal, it could result in unintended acceleration. The redundancy system is specifically designed to detect this disagreement and force a safe restricted-throttle state instead.

Does P0228 mean the sensor is always faulty?

Not necessarily. A short to the reference voltage in the wiring harness is equally common and will produce the same high-input symptom. Disconnect the sensor first — if the voltage drops, the sensor is the culprit; if it remains high, the fault is in the wiring.

Can a bad ground cause P0228?

Yes. If the sensor ground circuit is open, the signal pin loses its return path and may float toward the reference voltage, producing a spuriously high reading. Always verify sensor ground integrity as part of the diagnostic procedure.

How does P0228 differ from P0226?

P0226 is a rationality fault — the C-channel voltage is within the electrical range but does not agree with the A/B channels or engine conditions. P0228 is an absolute out-of-range fault — the signal voltage has exceeded the upper electrical threshold (typically above 4.5–4.8 V) and is considered electrically invalid regardless of throttle position.

Disabling P0228 in software

RaceTune can permanently disable P0228 — 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.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

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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