P0687 ECM/PCM Power Relay Control Circuit High

P0687 indicates a high condition in the ECM or PCM power relay control circuit. The relay control or feedback voltage is above the expected range.

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 overlook backfeed from added equipment when the PCM power relay circuit stays high.

Useful checks before replacing parts

Review relay command, control voltage, relay output, ignition state, battery voltage, freeze-frame data, and symptoms such as run-on or unexpected module power.
Inspect for short-to-voltage faults, open grounds, stuck relay contacts, backfeed from aftermarket wiring, corroded relay sockets, and fuse block damage.
Verify whether the relay control remains high when not commanded and whether PCM power feeds shut down correctly.

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.