P0812 Reverse Input Circuit

P0812 points to a reverse input circuit fault. The controller is not receiving a valid signal that indicates reverse selection or reverse-related input state.

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 diagnose reverse engagement mechanically until the reverse input signal has been confirmed.

Useful checks before replacing parts

Compare reverse input data with actual gear selection and check whether reverse lamps, backup camera, or shift logic respond correctly.
Inspect range switch, reverse switch, shifter wiring, connector condition, fuse feed, ground, and module input voltage.
Check whether the fault appears only in reverse, during shifter movement, after rain, or after transmission or console service.

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.