P0821 Gear Lever X Position Circuit

P0821 indicates a gear lever X position circuit fault. The side-to-side shifter position signal is invalid, missing, or outside expected limits.

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 transmission range sensor if the fault is isolated to the gear lever X position circuit.

Useful checks before replacing parts

Graph gear lever X position while moving the lever across gates and check for dead spots, jumps, or no movement in data.
Inspect the X position sensor circuit, shifter connector, reference voltage, ground, harness strain, and spilled-liquid damage.
Compare X and Y position signals to determine whether the fault is one axis or the whole shifter sensor assembly.

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.