Fault codeP0804

MODERATE

1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction

What this code means

1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction.

P0804 is a generic code: it means the same thing on every make. P0804 belongs to family P08xx — Transmission (continued). Its page explains how to read a code and groups all its codes by part.

Type of fault

The control unit has detected an electrical anomaly on this circuit without saying exactly which. Diagnosis starts with a visual check of the wiring and connector, then measuring the component — resistance, supply, ground — with a multimeter.

Dashboard signals from the engine control unit

The control unit drives some signals on the dashboard itself: the check engine light, the rev counter, the temperature warning or other warning lights. These codes mean it found a fault in one of these output circuits.

What you notice

A warning light that stays off or on, a rev counter that does not work; the engine runs normally.

How to check it

Check the connectors and the wiring between the control unit and the instrument cluster, and the cluster itself. On a modern car these signals often travel over the vehicle network: other modules may report communication codes at the same time.

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
8Transmission (continued)
04P0804