P0816 Downshift Switch Circuit

P0816 points to a downshift switch circuit fault. The manual downshift request input is stuck, missing, or not electrically plausible.

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 a shift solenoid from this code alone; it identifies the driver request circuit.

Useful checks before replacing parts

Monitor downshift switch status during paddle, lever, or button operation and check for clean transitions without dropouts.
Inspect shifter or steering-wheel wiring, switch contacts, connector corrosion, clock spring paths, reference voltage, and ground.
Compare upshift switch data and manual-mode status to see whether the fault is isolated or shared by the switch 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.