P0A92: Belt-driven generator speed disagrees with its prediction

GM's BAS hybrid P0A92 strategy assesses the mechanical drive-belt connection between the engine and motor-generator. It compares filtered, weighted predicted generator speed with filtered actual speed. The diagnostic is therefore specific to this drive arrangement, rather than a universal generator-output test.

Prediction and measurement must both be credible

The source requires the diagnostic system to be enabled and run/crank active. It also excludes specified crankshaft, coolant-temperature and air-related fault states. Those prerequisites matter because invalid reference information can undermine the expected-speed calculation.

The table prints a signed difference limit without a clear unit and contains inconsistent wording for one air-related prerequisite. This article does not invent a speed unit or resolve that label by assumption. Exact calibration information is needed for a numerical pass/fail decision.

A speed mismatch does not locate the mechanical fault

The code supports investigating the relationship between engine and generator motion. It does not, by itself, prove a broken belt, a specific tensioner fault or a failed generator sensor. Preserve both speed values, the operating state and companion faults for the prescribed diagnostic process.

Do not inspect or test a moving belt drive. Use the appropriate hybrid and mechanical service procedures. Verification should show credible predicted-versus-actual tracking and completed monitoring. A generator that charges briefly, or a code that has been erased, may not exercise the original speed-disagreement condition.

Source and applicability

2009 General Motors diagnostic parameter file 09OBDG08 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.

GM diagnostic parameters, PDF page 130.