P0A8E: Power-module overvoltage has hardware and software routes

P0A8E identifies excessive output voltage from the auxiliary power module in GM's BAS hybrid system. The table provides both hardware and software detection routes. Those routes use different voltage levels and time intervals, so there is no single universal duration that describes every triggering event.

Two paths protect against different event patterns

The hardware path uses a 20.9-volt overvoltage signal with a 20-millisecond interval. The software path evaluates output above 18 volts for two seconds. A short high peak and a lower sustained overvoltage can therefore meet different documented criteria.

These are calibration boundaries, not test targets. Do not deliberately raise system voltage to reproduce them. The monitor operates while the module is awake, and the code does not by itself reveal which path caused the stored result.

Preserve transient as well as steady-state evidence

A later ordinary battery-voltage reading cannot rule out a brief earlier overvoltage. Retain the failure record and any available module output history, along with companion voltage-sensor faults that affect interpretation.

The source does not establish a universal converter replacement or wiring repair from P0A8E alone. Use the exact hybrid service procedure to distinguish actual output behavior from measurement problems. Verification should include credible voltage information and completed monitoring under the prescribed conditions. Clearing the code cannot demonstrate that both transient and sustained overvoltage behavior have been corrected.

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 119.