P0804 1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction

P0804 points to a 1-4 upshift or skip-shift lamp control circuit malfunction. The warning or indicator circuit for skip-shift operation is not behaving correctly.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

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 bypass the skip-shift lamp circuit as a repair; verify whether the lamp, wiring, or control command is faulty.

Symptoms of P0804

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0804

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Check skip-shift lamp command, bulb or cluster input, circuit voltage, fuse feed, ground path, and connector condition.
Compare skip-shift solenoid command, clutch switch, vehicle speed, throttle, and gear inputs with the lamp command.
Inspect wiring between the powertrain controller, cluster, and transmission-related controls for opens, shorts, or corrosion.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.