P2B98: low supply to the exhaust pressure valve motor

The cited P2B98 monitor asks whether the exhaust throttle valve DC motor is correctly supplied. Its failure criterion is driver/system supply below 6 volts, reported by the hardware input/output layer. Separately, the powertrain relay supply must be above 11 volts for the diagnostic to operate.

The two supplies are different evidence

The comparison of local motor supply with the qualified relay supply is more informative than the phrase “low voltage” alone. A healthy upstream voltage does not prove that the motor driver receives adequate power. Conversely, a reading taken during cranking is outside this monitor's listed operating phase.

Confirmation requires 240 failed counts out of 300 samples at a 12.5-millisecond task interval. The hardware error status must be determinate, and no diagnostic reset or end-of-trip inhibition may prevent evaluation.

Use supply evidence before judging the valve

A motor unable to obtain adequate supply may not respond correctly to a position request. Establish the supply behavior before treating a stationary exhaust valve as proof of a mechanical jam. The table does not isolate the voltage loss to a particular connector, wiring segment or internal electronic component.

Verification should demonstrate adequate motor supply during commanded operation with a valid hardware status and a completed monitor. A battery voltage reading taken elsewhere or with no motor demand does not answer the local supply question. Any access around the exhaust actuator must follow the relevant hot-component and moving-actuator service precautions.

Source and applicability

Documented 2025 GM gm-2025-04b monitor only; vehicle, engine and controller applicability must be established separately. GM monitor table, PDF page 1533.