P0629: fuel-pump relay output stays high while commanded off

P0629 is an off-state short-to-power check of the feed-fuel-pump relay high-side driver in the selected 25OBDG04B monitor. The controller identifies an abnormal voltage response when the output is powered off.

Command state separates this from the low-circuit test

The source characterizes the short as impedance of 0.5 ohm or less between the signal and controller power. Unlike the on-state P0628 check, this diagnosis concerns an output that should no longer be driven. A voltage trace without the request state cannot settle that distinction.

The failure filter uses eight failed samples among ten at 250 ms per sample, with Type A reporting. The supply-enable column mentions 11 V but does not publish a clear inequality, so the exact service definition remains necessary.

An accompanying open-circuit code may be related

The row explicitly notes that certain controllers can also set P0627. Concurrent codes do not automatically prove independent faults or identify a defective pump motor.

Verification should demonstrate the correct off-state response and follow the vehicle-specific relay-control diagnosis to locate the electrical cause. The impedance figure is a failure characterization, not an energized-circuit meter instruction. This article deliberately confines its criteria to 25OBDG04B; other controller implementations may use different timing and voltage thresholds for the same code.

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 625.