P0891 TCM Power Relay Sense Circuit High

P0891 indicates a high TCM power relay sense circuit signal. The relay feedback voltage is higher than expected or present when it should not be.

Code status

Needs verification

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

System: Transmission
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 replace the TCM until the relay sense circuit is checked for backfeed or stuck relay contacts.

Useful checks before replacing parts

Check for short-to-voltage, stuck relay contacts, incorrect relay installation, damaged wiring, and sense circuit faults.
Compare relay command with relay output and sense voltage when the relay should be off and on.
Inspect aftermarket wiring, fuse-panel corrosion, and repaired harness sections that can backfeed the sense circuit.

Related OBD-II codes

These nearby transmission entries can help compare wording and fault area. They may share the same verification status as the source database.