P23C4Engine Coolant Bypass Valve C Position Sensor Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P23C4 says the angle reported by the bypass valve C position sensor has dropped below anything the sensor can produce in normal use, which GM traces to the signal line touching ground. GM's 2025 tables use the code on both its 3.0L Duramax diesel (25OBDG04B) and a gasoline family (25OBDG03B): the SENT sensor value must fall under 27 or under 50 counts respectively, for 4 seconds within a 5-second window, while SENT communication itself is healthy and the engine is not cranking. It is a Type B fault, so the lamp comes on after the second failing trip. With the feedback gone, the valve can no longer be positioned reliably and warm-up or cooling may suffer. The opposite case is P23C5; a wider position error is P26BB.
- What you may notice
- Engine warning lamp after two drives
- Bypass valve C position shown as implausibly low in live data
- Slow warm-up or unusual engine temperature
- Likely causes
- LikelyPosition sensor signal wire chafed against ground
- PossibleCoolant or water in the valve connector bridging the signal to ground
- PossibleDefective position sensor inside the valve actuator
- RareMissing sensor supply so the output stays at its lowest value
- 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.