P23C4: coolant bypass valve C digital position signal low

P23C4 is a low-signal diagnosis for the position sensor of engine coolant bypass valve C. The cited implementation receives a SENT digital position value. Its failure threshold is below 27 digital counts; that number is neither degrees of valve movement nor a connector voltage.

Valid communication can carry an invalid position

The monitor requires SENT communication not to be in error. It then evaluates whether the reported position lies outside the expected range, describing the low condition as a signal-circuit short to ground. The distinction matters: a lost digital message and a valid message carrying an out-of-range value are separate fault paths.

Run/crank must be valid, the engine must not be cranking and the diagnostic system must be enabled. The low value must persist for four seconds in a five-second window. Reporting is Type B, two trips.

Useful diagnostic evidence

Review position data and SENT communication status together. A generic voltage measurement does not reproduce the digital-count criterion without the specific service information. Similarly, a coolant-temperature complaint cannot establish this electrical failure. Verification should show that the position stream remains valid and passes its range check under enabled conditions. The source does not identify a physical valve location or establish that the valve assembly itself is the only possible cause.

Source and application limits

This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 819.