What P0804 means
1–4 Upshift (Skip Shift) Lamp Control Circuit Malfunction
How to diagnose
- Read freeze frame data. When P0804 set, your ECU snapshotted every sensor at that moment. This tells you what the car was doing when the fault triggered — RPM, load, coolant temp, throttle position, fuel trims. Almost always enough info to figure out the cause without further testing.
- Check for related codes. If you have P0804 plus other codes, fix the earliest one in the chain first — a single root cause often triggers multiple codes.
- Cheap fixes first. For most codes, the order is: inspect connectors + wiring (free), check for vacuum leaks (cheap), replace sensor (moderate), replace mechanical part (expensive). Follow that ladder before dropping money on parts.
Manufacturer-specific descriptions
Different manufacturers use P0804 for slightly different failure modes:
| BMW | 1-4 Upshift (Skip Shift) Lamp Control Circuit |
| FORD | 1 - 4 Upshift (Skip Shift) Lamp Control Circuit Malfunction |
| MITSUBISHI | 1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction |
| NISSAN | 1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction |
| VOLKSWAGEN | 1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction |
Read P0804 on your own car
DIY Fix My Car reads P0804 plus 25,000+ other DTC codes with manufacturer-specific descriptions. Includes freeze frame data, likely fix parts, and AI mechanic chat. Download free.