P2261: Turbo bypass valve fails the coast-down pulsation check

P2261 indicates a compressor recirculation valve stuck-closed signature in the reviewed GM turbocharger strategy. The source explicitly limits this row to a turbocharger with wastegate, excluding a supercharger with a mechanical compressor despite the broader dictionary title.

The controller evaluates the response to opening

During coast-down lift-off, the monitor looks for airflow pulsation while the bypass valve is commanded open. The documented command must exceed 6% duty cycle for at least 0.25 second, with engine speed at or above 1,500 rpm and additional compressor-pressure and transient conditions satisfied.

The failure calculation includes accumulated filtered airflow above 70 g/s within its calibrated measuring period. The table also lists a boost-pressure-derivative branch with a very high threshold; this summary does not assume both branches contribute equally on every calibration.

A command is not proof of movement

An open command accompanied by the expected airflow response is different evidence from the command alone. This is why an electrical circuit check can pass while a mechanical-performance monitor still finds a problem.

Conversely, related bypass-circuit, boost-sensor and airflow-sensor fault groups inhibit the test. Their presence changes the confidence that can be placed in a missing or incomplete P2261 result.

The decision requires four failed tests out of five, with 25-millisecond sampling, and is classified Type B, two trips. Verification needs an eligible monitored event and acceptable response using the applicable service procedure. The code does not authorize replacing the turbocharger assembly or identify a specific mechanical obstruction.

Source and applicability

The documented system and calibration must be confirmed for the vehicle before using these limits. GM diagnostic table, PDF page 626.