P048A: exhaust throttle fails its spring-return position check

P048A evaluates the exhaust throttle after its electrical drive has been removed. The cited system expects a fully open default and reports a stuck-closed condition if measured position stays below 70% after the specified wait.

The sequence begins with P0476

The position-performance code P0476 must already be set. The return check waits more than two seconds after driver shutoff, allowing the spring to move the valve toward default. The result is therefore a follow-on mechanical-response assessment, not an ordinary position comparison during active control.

The threshold also clarifies the label: the monitor does not require a completely closed, zero-percent reading. Failure to return sufficiently far toward open can meet its criterion.

Evidence needed for a useful conclusion

The diagnostic system must be enabled and the listed position-sensor, valve and deviation status gate satisfied. No additional debounce applies once the error is present; the function task is 6.25 ms and reporting is Type A.

Retain the preceding P0476 event, shutoff timing and valid post-wait position. A reading taken before the spring-return interval is not comparable. Verification should establish correct default return using the applicable service procedure. The table does not identify a particular obstruction, prove a pressure-related failure or authorize forcing a hot exhaust throttle mechanism.

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 1201.