Faulty or blown bulb or LED in the instrument cluster indicator; Damaged wiring, chafing or open circuit between the control module and the instrument cluster; Corroded, loose or pushed-out pins at the cluster or control module connectors; Short to earth or to supply voltage in the lamp control wire; Fault in the instrument cluster circuit board or its lamp driver; Internal lamp driver fault in the engine or powertrain control module; Outdated or faulty control module software, where the manufacturer has a known fix for the model.

P0804

Upshift/Skip Shift Lamp Control Circuit.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
8: AreaTransmission
04: FaultThe specific fault in that area

What it means

P0804 is a generic powertrain code for a fault in the control circuit of the upshift or skip shift lamp, the dashboard indicator that tells the driver when to change up on a manual gearbox. The engine or powertrain control module drives the lamp and monitors the circuit. It set the code because the voltage or current it saw did not match what it commanded, which points to an open circuit, a short or a faulty lamp or driver.

Symptoms

Upshift or shift indicator lamp stays on all the time
Upshift or shift indicator lamp never lights
Lamp flickers or lights at the wrong moments
Malfunction indicator lamp may be on
Gearbox and engine otherwise drive normally

Possible causes

Faulty or blown bulb or LED in the instrument cluster indicatorlikely
Damaged wiring, chafing or open circuit between the control module and the instrument clusterlikely
Corroded, loose or pushed-out pins at the cluster or control module connectorspossible
Short to earth or to supply voltage in the lamp control wirepossible
Fault in the instrument cluster circuit board or its lamp driverpossible
Internal lamp driver fault in the engine or powertrain control modulerare
Outdated or faulty control module software, where the manufacturer has a known fix for the modelrare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note whether other cluster or communication codes are present
Check the lamp behaviour at ignition on and during a bulb check, noting if it is stuck on, stuck off or intermittent
Inspect the wiring and connectors between the cluster and the control module for chafing, water ingress, corrosion and bent or loose pins
Check for any recent work, aftermarket fittings or damage near the dash or harness that could have disturbed the circuit
Use the wiring diagram for the model to identify the lamp control wire, then test it for continuity, short to earth and short to voltage with the ignition off and the module disconnected
With the ignition on, check the supply and the control signal at the cluster, and compare with the specification for that vehicle
Command the lamp on and off with a scan tool's output test, if the model supports it, to see if the driver and lamp respond
Check for manufacturer service bulletins or software updates for the specific model and engine

How to fix

Replace the faulty bulb or the cluster indicator if the lamp itself has failed
Repair or replace damaged wiring and fix any short or open circuit found
Clean, re-seat or replace corroded or damaged connectors and terminals
Repair or replace the instrument cluster if its lamp driver or circuit board is faulty
Replace or repair the control module only after the wiring and cluster have been proved good
Apply a manufacturer software update if a known fault in the calibration is confirmed for that model

Can I keep driving?

Low severity

The car can normally be driven as the fault only affects a shift indicator, but book it in soon. Change gear by feel and sound rather than relying on the lamp, and have it checked if other warning lamps appear or the car drives differently.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.