P23C5Engine Coolant Bypass Valve C Position Sensor Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- With P23C5 the position feedback of coolant bypass valve C sits at the top end of its digital range, a reading GM explains as the signal line touching a voltage source. In GM's 2025 summaries for the 3.0L Duramax (25OBDG04B) and a gasoline engine family (25OBDG03B) the limit is identical: a SENT value above 4,050 counts present for 4 seconds within 5 seconds, checked only when the SENT link reports no error and the engine is not cranking. GM rates it Type B, two trips to the lamp. A high reading can also come from a broken ground at the sensor. Until it is fixed the module cannot trust the valve angle, so coolant routing may be wrong. Low readings are P23C4, general circuit faults P23C3.
- What you may notice
- Engine warning lamp on the second faulty trip
- Live data shows bypass valve C near full scale regardless of command
- Heater output or engine temperature behaves unusually
- Likely causes
- LikelyPosition signal wire shorted to a supply or reference wire
- PossibleOpen ground wire of the position sensor
- PossiblePosition sensor in the valve actuator reporting a stuck maximum value
- RareBent or spread terminals in the valve connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.