Powertrain, generic (extended)

P23C4 Engine Coolant Bypass Valve C Position Sensor Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Position sensor signal wire chafed against ground
Coolant or water in the valve connector bridging the signal to ground
Defective position sensor inside the valve actuator
Missing sensor supply so the output stays at its lowest value

Symptoms

  • Engine warning lamp after two drives
  • Bypass valve C position shown as implausibly low in live data
  • Slow warm-up or unusual engine temperature

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

P23C3P23C5P26BBP26A6P2AA9

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