Powertrain, generic (extended)

P23C5 Engine Coolant Bypass Valve C Position Sensor Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Position signal wire shorted to a supply or reference wire
Open ground wire of the position sensor
Position sensor in the valve actuator reporting a stuck maximum value
Bent or spread terminals in the valve connector

Symptoms

  • 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

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

coolant bypass valve c position sensor

Related codes

P23C3P23C4P26BBP26A7P2AAA

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.