P0477: exhaust throttle command short-to-ground detection

P0477 is an electrical short-to-ground check of the exhaust throttle command circuit in the cited implementation. The controller uses hardware-reported H-bridge overcurrent while the driver is on.

The threshold belongs to current

The failure boundary is above 8 A. “Low” in the generic circuit label should not be converted into a guessed voltage limit, nor does it mean exhaust pressure is low. The monitored signal is the driver's electrical fault status associated with excessive switch current.

The diagnostic requires relay supply above 11 V and an engine outside cranking. It also needs an enabled diagnostic system and determinate hardware status. The listed filter is 240 failed counts out of 300 samples on a 12.5 ms task, with Type A reporting.

Verification follows the operating state

An on-state overcurrent event and an off-state open-load event answer different questions. Preserve the drive command with the failure record so that a later test can be compared with the correct state.

After service, establish normal electrical response during an eligible drive interval using the applicable procedure. Current magnitude alone cannot identify the short's location or distinguish every internal actuator fault from wiring trouble. The source does not provide a pinout, replacement verdict or safe direct-power test. Avoid treating the monitor threshold as a specification for manually loading the actuator circuit.

Source and applicability

2025 GM 25OBDG04B diagnostic parameter tables; the cited monitor only. Vehicle, engine and calibration applicability must be confirmed separately. These tables describe detection logic, not a complete repair procedure or a component replacement verdict. gm-2025-04b, PDF page 1198.