P26CE: Pump overspeed is a filtered mismatch, not proof of trapped air

P26CE evaluates coolant-pump feedback running faster than the requested speed. GM forms a filtered command-minus-feedback difference; overspeed makes that difference negative. This is a tracking diagnosis, so an absolute speed reading without its requested value cannot reproduce the decision.

Preserve the stable-command window

The source requires the command to change by less than 50 rpm for at least three seconds. It also lists pump enablement, a minimum command of 300 rpm and supply eligibility. These conditions distinguish a sustained tracking discrepancy from ordinary changes while the controller is accelerating or decelerating the pump.

Failure confirmation uses eight seconds within a ten-second window. The result is therefore not equivalent to one fast-looking feedback sample. Preserve the command, feedback and their filtered relationship across the qualifying interval.

Do not turn placeholders into specifications

The table names different overspeed thresholds for voltage branches but does not supply usable numerical values for those thresholds. It also prints a −9,999 V dividing value, which cannot be treated as a physical vehicle-voltage instruction. Those unresolved entries prevent reconstructing the complete calibration from this summary.

The supported conclusion is a sustained overspeed tracking classification. Although the generic label mentions air in the system, this monitor does not independently confirm trapped air or prescribe bleeding. Vehicle-specific cooling-system checks are needed to determine the cause without substituting a label for evidence.

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 851. 25OBDG03B, PDF page 852.