P26C0: A coolant valve is classified open only after target error is established

P26C0 describes the engine-block coolant rotary valve being classified as stuck open in this GM monitor. Its decision needs two facts together: requested position and feedback differ enough, and the reported position falls on the high side of a calibrated boundary. Position alone is not the complete test.

A tracking error plus a position boundary

The absolute target-versus-feedback error must reach at least five degrees, while feedback is at least 50 degrees. The controller requires that failure pattern for four seconds within a five-second window. A brief movement through 50 degrees therefore does not, by itself, establish the fault.

Eligibility includes adequate system voltage, a commanded-on powertrain relay and usable feedback without relevant circuit faults. The requested valve position must also be inside the documented operating range. These conditions prevent an invalid signal or unavailable drive supply from being treated as an ordinary mechanical tracking comparison.

Verify the trajectory rather than an isolated angle

Useful evidence aligns target angle, measured angle and enable state through the observation window. A valve can be near an endpoint because it was requested there; the target error is what distinguishes that ordinary condition from the monitored failure.

The criteria classify behavior within this calibration’s endstops. They do not directly measure coolant flow or locate a jam. Confirm the relevant command and feedback behavior before pursuing the vehicle-specific electrical or mechanical procedure.

Source and applicability

2025 GM 25OBDG03B documented monitor only. Vehicle, engine and calibration applicability must be confirmed from the matching service information; no model fitment is inferred. These criteria explain controller logic, not a complete repair procedure. 25OBDG03B, PDF page 847. 25OBDG03B, PDF page 848.