P0689: relay feedback remains low when the relay is on

P0689 checks the control-module power relay's feedback voltage. In the cited GM calibration, relay voltage at or below 5 volts is a failing observation while the powertrain relay state is ON.

Compare feedback with the enabled supply context

Run/crank voltage must exceed 9 volts before this monitor runs. The comparison therefore concerns inadequate relay feedback despite a sufficiently high enabling supply, rather than every low-voltage condition in the vehicle. Record the two voltages together when available.

The controller requires five failed samples out of six at one second per sample. A short switching transient and a sustained feedback failure can therefore have different outcomes. The source does not define this as an immediate reaction to any single low reading.

Control and feedback are different evidence

This code is not the low-side relay control-circuit monitor. It asks whether the sensed relay voltage is low in the on state. The driver command may be present even when the observed feedback is inadequate, and the row does not identify which part of that relationship failed.

Verification should show appropriate feedback with the relay on and completion of the enabled monitor, using the exact vehicle service procedure. Merely changing a relay command PID is not enough. The table supplies no relay location, expected load current or automatic relay-replacement rule. Its Type B/two-trip classification does not remove the need to investigate the recorded power-feedback failure.

Source and applicability

Documented monitors in gm-2025-03a, model year 2025. These are module/calibration examples; vehicle, engine and transmission applicability must be confirmed independently. GM 2025-03a, page 420.