1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction
P0804 indicates a malfunction in the skip shift lamp control circuit, which is responsible for illuminating the upshift indicator light that tells drivers when to shift gears for optimal fuel economy. The code sets when the powertrain control module detects an electrical problem with the lamp circuit, such as an open, short, or communication failure.
What You Might Notice
- Skip shift indicator lamp is inoperative or does not illuminate
- Skip shift indicator lamp remains on constantly or flashes unexpectedly
- Skip shift function is disabled or not working properly
- Transmission may enter limp mode or reduced power mode
- No warning lights on instrument cluster related to transmission
Most Common Causes
- 1
Defective skip shift lamp bulb
The indicator bulb in the dashboard has burned out or failed, preventing the skip shift message from displaying to the driver.
- 2
Shorted or open wiring in lamp circuit
The electrical wiring between the transmission control module and the skip shift lamp has a break, corrosion, or unwanted connection causing circuit malfunction.
- 3
Faulty connectors or loose connections
Corroded, damaged, or loose electrical connectors at the lamp or control module prevent proper signal transmission.
- 4
Transmission control module programming error
The transmission control module software contains a corruption or calibration issue that prevents it from properly controlling the skip shift lamp circuit.
How to Diagnose It
- 1
Check Defective skip shift lamp bulb — The indicator bulb in the dashboard has burned out or failed, preventing the skip shift message from displaying to the driver.
- 2
Check Shorted or open wiring in lamp circuit — The electrical wiring between the transmission control module and the skip shift lamp has a break, corrosion, or unwanted connection causing circuit malfunction.
- 3
Check Faulty connectors or loose connections — Corroded, damaged, or loose electrical connectors at the lamp or control module prevent proper signal transmission.
- 4
Check Transmission control module programming error — The transmission control module software contains a corruption or calibration issue that prevents it from properly controlling the skip shift lamp circuit.
How to Fix It
- 1
Replace skip shift indicator lamp bulb
Access the dashboard instrument cluster and replace the burned-out or failed skip shift indicator bulb with a new one of the correct type and wattage.
- 2
Inspect and repair lamp circuit wiring
Visually inspect the wiring harness from the transmission control module to the skip shift lamp for cuts, corrosion, or pinches. Repair or replace damaged sections as needed.
- 3
Clean or replace electrical connectors
Remove and inspect all connectors in the skip shift lamp control circuit for corrosion or damage. Clean with contact cleaner or replace connectors if corroded or broken.
- 4
Reprogram or replace transmission control module
If wiring and connectors are good, the transmission control module may need reprogramming with updated software or replacement if the module itself is defective.
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