OBD-II - Throttle Position Sensor/Switch C Circuit High Input

P0229 Diagnostic Guide (OBD-II) - Throttle Position Sensor/Switch C Circuit High Input

Overview

• Definition (common across manufacturer literature variants): P0229 indicates a fault in the Throttle Position Sensor (TPS) Switch C circuit - specifically a high input on the Switch C channel. This is part of the throttle pedal position sensing system (often with multiple switches labeled A, B, C) used by the PCM to monitor pedal/throttle position.
• What the PCM does: When a high input is detected on TPS Switch C that is out of expected range or inconsistent with other throttle position signals, the PCM stores P0229 and often illuminates the MIL (check engine light). This fits the general principle that OBD-II powertrain diagnostics monitor sensor circuits and set codes when abnormal conditions are detected.
• Related reference: The Open Source OBD2 definition for this symptom cluster identifies the concept as i.e., the pedal-position sensor's Switch C with intermittent signal. This supports the interpretation that Switch C is a discrete channel used by the PCM to verify throttle pedal position.

Probable Causes

Because do not include NHTSA complaint data, I'm listing probable causes with field-experience weights rather than manufacturer-specific deltas. Use these as a starting framework and confirm with measurements.

• TPS Switch C sensor or connector fault (most frequent)
  • Likely causes: defective Switch C electronics in the pedal assembly, worn internal contacts, intermittent signal due to aging, or a corroded/loose connector on the Switch C wire.
  • Estimated probability in field practice: 40-50%
  • Related wiring harness or connector issues (see next item) can manifest as intermittent high inputs.
• Wiring harness damage or poor/loose connections on the Switch C circuit
  • Includes damaged insulation, chafed wires, bent pins, corrosion in the connector, or harness routing that pulls on the C-channel lead.
  • Estimated probability: 20-25%
• PCM/ECU fault or misinterpretation of the C input (less common)
  • Could be caused by a software fault, a damaged input circuit inside the ECU, or a transient condition that the ECU misreads as a fault.
  • Estimated probability: 5-10%
• Power/ground reference issues or interference on the Switch C circuit (high input due to signal reference disturbance)
  • Could be caused by a failing reference (5V) supply to pedal sensors, poor ground, or electrical noise.
  • Estimated probability: 5-15%
• Mechanical throttle-body issues or pedal assembly binding (less common as a direct cause, but may produce symptoms that mimic a sensor fault)
  • Estimated probability: 5-10%
    Note: These percentages reflect a typical mix observed in ASE-style diagnostics and general field experience rather than a specific dataset.

Safety and precaution notes

• P0229 can be accompanied by other TPS-related codes (e.g., P0220, P0223, etc.) depending on how many position-sensing channels the system uses. Treat simultaneous TPS-related codes as a sign to review both the sensor and the wiring, not just a single channel.
• When performing live data checks, avoid probing while the engine is running in an unsafe environment. Use proper PPE and disconnect fuel/injector risk shop's safety protocol.
• After any sensor or wiring repair, follow the manufacturer's recommended throttle/TP relearn or calibration procedure if required for your vehicle.

Diagnostic Approach

1) Verify and document

• Confirm P0229 is current and note any freeze-frame data (if available): throttle position percent, pedal position readings, and engine load when the code was logged.
• Check whether the MIL is steady or intermittent.

2) Visual inspection and basic diagnostics

• Inspect the pedal-position sensor assembly and the Switch C connection for signs of damage, corrosion, bent pins, or loose connectors.
• Inspect the wiring harness for chafing, melted insulation, or routing that could cause intermittent contact.
• If accessible, inspect the connector seals and moisture exposure.

3) Baseline electrical checks

• Power and ground:
  • With the ignition ON (engine OFF), verify that the 5V reference to the pedal-position sensor is present and stable, and that the sensor ground is solid.
  • Confirm there is a clean, low-resistance ground path back to the PCM/ECU.
• Signal integrity:
  • Using a DVOM or the scan tool's live data, observe the Switch C signal when you cycle the pedal from idle (0%) to full throttle (100%). Note whether Switch C shows a valid change and whether it tracks with pedal position or behaves abnormally (stuck high, jitter, or random spikes).
• Compare with other TPS channels:
  • If the vehicle uses multiple TPS channels (A/B/C), compare their signals for consistency with pedal position. A healthy system should show correlated movement across A/B/C with no one channel acting erratically.

4) Targeted testing of Switch C circuit

• Backprobe the Switch C signal wire at the pedal assembly connector and measure:
  • Signal voltage relative to ground (should be within the expected range for a high input when Switch C is asserted).
  • Continuity from pedal connector to PCM input to ensure there is no open circuit.
• Check for cross-talk or intermittent contact by gently wiggling and tapping the harness and connectors while monitoring the Switch C input for changes or dropouts.

5) Isolate the fault

• If Switch C signal is defective or intermittent:
  • Repair/replace the pedal-position sensor assembly or its Switch C circuit as appropriate.
  • If the issue is a connector or wiring fault, repair the harness (re-crimp, replace connector housing, or replace wires) and reseal as required.
• If wiring/connector checks pass and Switch C signal is clean but P0229 persists:
  • Consider replacing the pedal-position sensor or Switch C module, and recheck with a test drive.
• If all sensors and wiring test good, and the code still returns:
  • Investigate the PCM input circuit for potential fault or the need for ECU programming or calibration in accordance with vehicle-specific service information.

6) After repair: code reset and test drive

• Clear the codes with the scan tool and perform a complete drive cycle (including idle, light acceleration, and steady-state cruising) to confirm the code does not return.
• If the vehicle requires a throttle relearn or adaptation after sensor or connector replacement, perform the relearn procedure per the manufacturer's procedure.

Recommended repairs (typical)

• Clean or repair the Switch C connector and wiring, reseal as needed.
• Replace the pedal-position sensor assembly or Switch C module if electrical symptoms persist after wiring repair.
• Repair or replace damaged harness sections (short to power or ground, or intermittent contact).
• If ECU-related (less common) and the issue persists after sensor and harness repairs, consult OEM service information for ECU fault diagnostics or programming/lock-in procedures.
• After a repair, follow any manufacturer-recommended throttle body relearn/initialization procedures.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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