P0489: high-pressure EGR short-to-ground current signature

P0489 is the high-pressure EGR command short-to-ground check in this GM implementation. Hardware information reports excessive current through the H-bridge switches while the driver is commanded on.

Interpreting circuit low

The actual threshold is current above 8 A. The generic word “low” identifies the fault category, not a low EGR flow rate or a published low-voltage limit at a connector. That distinction changes the relevant diagnostic evidence from airflow to actuator electrical behavior.

The monitor runs outside cranking with relay supply above 11 V, enabled diagnostics and determinate hardware status. It uses a 240-of-300 failure filter on a 12.5 ms task and Type A, one-trip reporting.

Separate the command states

This on-state check differs from P0403's off-state open-load assessment. An electrical observation must be interpreted against the state in which it was obtained; an unpowered reading does not by itself reproduce the current fault.

Verification should demonstrate normal drive-circuit response in an eligible operating interval and follow the correct service isolation procedure. The published current criterion does not locate the short or prove the EGR valve itself has failed. It supplies no pinout, resistance test or instruction to defeat the driver protection. Confirm vehicle and calibration applicability before using the threshold as diagnostic context.

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 1200.