Powertrain, generic (extended)

P23C6 Engine Coolant Bypass Valve C Control Circuit Driver Current/Temperature Too High

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

P23C6 is set by the output stage itself: the H-bridge that drives the motor of coolant bypass valve C reports more current, or more heat, than it can tolerate. GM labels it a motor overcurrent in two 2025 summaries, the diesel table 25OBDG04B (3.0L Duramax) and the gasoline table 25OBDG03B; the driver flags it while energized, with a controller-specific trip point listed between 8.1 and 12.8 A, and the code matures after 2 seconds within 5 seconds as Type B. Typical triggers are a seized valve rotor, a motor with shorted windings or a partial short in the motor wires. To protect itself the driver switches off, so the valve stays where it is. Open and shorted motor circuits are P26B7 to P26B9.

Likely causes

Valve rotor stiff or seized by deposits or worn seals, so the motor stalls

Shorted windings in the valve motor drawing excess current

Motor wires partly shorted to each other or to ground

Overheated or faulty H-bridge driver in the engine control module

Symptoms

Engine warning lamp after two trips
Bypass valve C no longer moves and stays in its last position
Engine runs too cold or too warm depending on where the valve stopped

Repair estimate

DifficultyHardWorkshop job

Parts and labour€150–1,100

Time1–4 h

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

Parts involved

coolant bypass valve c

Related codes

P26B7 P26B8 P26B9 P26BB P23C3

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