P0689 ECM/PCM Power Relay Sense Circuit Low

P0689 points to a low condition in the ECM or PCM power relay sense circuit. The module sees relay output voltage below the expected level.

Code details

Generic OBD-II · P0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not ignore voltage drop across fuse box or relay terminals when the sense circuit reads low.

Symptoms of P0689

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of P0689

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Measure power relay output and sense voltage at the relay and PCM, then review battery voltage, grounds, ignition state, and freeze-frame conditions.
Inspect for high-resistance relay contacts, weak battery supply, corroded fuse block terminals, damaged sense wiring, open feeds, and poor module grounds.
Load-test the relay output while monitoring the sense circuit to identify voltage drop under actual module load.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.