P026A: charge-air cooling efficiency falls below the calibrated result

P026A evaluates charge-air-cooler thermal efficiency in this GM monitor. Efficiency is the upstream-to-downstream air-temperature drop divided by the upstream-to-reference temperature difference. The averaged result fails below 42 percent, after the strategy applies its calibrated sample corrections.

The reference depends on the architecture

The source supports air-cooled and water-cooled applications. Calibration selects outside air, induction air or cooler-inlet coolant as the reference temperature. Using outside air indiscriminately could therefore produce a different calculation from the ECM's actual test.

The monitor averages 160 samples in a 100-millisecond task. Its prerequisites include vehicle speed above 30 km/h, compressor pressure ratio above 1.25 and more than 50°C between upstream charge air and the selected reference. Temperature-sensor and other supporting faults must be absent; enable conditions must persist for at least four seconds.

What the result narrows

A low efficiency result is a thermal comparison, not direct proof of a leaking charge pipe or a failed water pump. Preserve all three relevant temperatures and the selected reference. Incorrect input information can invalidate an independent calculation even when the displayed cooler temperatures appear plausible.

Verification requires a completed eligible efficiency evaluation, with the architecture's applicable conditions met. A low-load idle check cannot reproduce the specified thermal opportunity. This Type B, two-trip monitor does not by itself identify the cooler component requiring repair.

Source and applicability

GM 04B, PDF page 1121; GM 04B, PDF page 1122; GM 04B, PDF page 1123. This explanation covers the documented 2025 monitor. Confirm the vehicle's module, engine and calibration before applying these criteria; the document's vehicle list does not establish this code's applicability to every listed model.