P050A: cold-start idle error during catalyst heating

P050A assesses idle-speed control during the catalyst-heating phase after a cold start. The source includes both overspeed and underspeed branches, so the generic performance label does not specify which direction the engine speed deviated.

The sign of the error matters

The error is desired speed minus current speed. The overspeed branch uses a value below −200 rpm, while the underspeed branch uses a value above 100 rpm. Both list ten-second qualification and two-trip reporting.

This sign convention prevents a common misreading: a negative desired-minus-actual result means actual speed is above the request. It is not an underspeed value merely because it is negative.

A dedicated operating phase

The monitor requires completed engine start, active relevant catalyst heating, zero vehicle speed, valid crankshaft information, and no relevant limp-home or safety-cutoff operation. The shown coolant window is −12°C to 66°C, with at least two seconds after end of start. No torque demand is also part of the listed state.

A normal warm idle after catalyst heating has finished does not verify this cold-start phase. Confirmation should establish which speed-error branch failed and show acceptable tracking during a completed eligible heating interval. The table identifies control performance but does not select an air-path, ignition, or fuel-system repair.

Documentation and applicability

These details describe the monitor in GM’s 2025 25OBDG07A Part2 file. Its application-matrix filename does not match the download index, so model and engine applicability remain unresolved. Use the vehicle’s correct service information before applying these calibration details.

GM diagnostic table, PDF page 533; GM diagnostic table, PDF page 532.