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 status

Needs verification

Not yet verified against SAE J2012_202509 / J2012DA. Treat unverified rows as a lookup aid, not repair authority.

System: Computer
Scope: iso-sae-controlled-p0
Standard: SAE J2012 / ISO 15031-6
Source: legacy-import

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.

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 fault area. They may share the same verification status as the source database.