P26C2: Low-side coolant-valve position must also miss its target

P26C2 is the closed-side classification of a coolant rotary valve tracking failure. GM first compares the requested and measured angles, then uses the feedback position to distinguish this result from the open-side classification. A low valve angle during a matching low-angle command is not sufficient evidence of a fault.

Read both parts of the decision

The absolute position error must be at least five degrees and the feedback angle below 50 degrees. The calibration requires four seconds of failure within a five-second observation window. A momentary lag as the target changes is therefore different from the completed monitored event.

System-voltage eligibility, powertrain-relay state and valid position feedback also matter. Relevant feedback circuit faults must not be pending or active. If the feedback channel is electrically unreliable, interpreting its angle as a definite mechanical position would bypass an important qualification in the source.

Separate a commanded position from failed movement

Retain the target, actual angle and their difference over time. The useful question is whether the valve remains on the closed side while failing to follow an eligible request, not merely whether a scan display shows a small number.

The monitor operates within calibrated mechanical endstops and does not directly prove inadequate coolant circulation. A matching service procedure is needed to determine whether the observed failure involves the mechanism, drive conditions or feedback path. The code alone does not select a thermostat or valve replacement.

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 849. 25OBDG03B, PDF page 850.