P2B99: exhaust valve H-bridge temperature above its limit

The generic P2B99 description combines driver current and temperature, but this GM implementation specifically monitors H-bridge driver temperature. The documented threshold is above 170°C, with hardware input/output circuitry supplying the error information. It is not an exhaust gas temperature threshold.

Identify the temperature being diagnosed

An H-bridge is the electronic drive stage for the valve's DC motor. Its thermal diagnosis concerns that drive electronics, even though the actuator operates in an exhaust system. The source mentions internal motor faults as an example of a possible contributor, but the code does not establish one particular cause.

The controller requires 240 failing observations out of 300 samples at a 12.5-millisecond task rate. It evaluates outside cranking, with powertrain relay voltage above 11 volts, the diagnostic enabled and a determinate hardware error state.

Reconstruct the operating demand

A useful record combines the thermal fault status with valve command history and movement response. Repeated drive effort without appropriate motion and a thermal event during otherwise ordinary motion are different diagnostic observations. Neither should be converted into a replacement instruction without the applicable electrical and actuator procedure.

Verification requires the thermal monitor to complete under representative valve operation. Cooling the system until the fault disappears proves only that the immediate temperature condition changed; it does not establish why the driver overheated. The table provides no safe surface-temperature estimate and no instruction to touch or dismantle a hot actuator.

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 1534.