1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction
The P0804 code indicates a malfunction in the control circuit of the 1-4 upshift (skip shift) lamp. This system is designed to improve fuel economy by forcing the transmission to skip from 1st to 4th gear under certain conditions, and the lamp illuminates to inform the driver. The circuit includes the lamp, wiring, and the powertrain control module (PCM). A fault can be due to a burned-out bulb, damaged wiring, or a faulty PCM.
01. Most Common Causes
- Burned-out 1-4 upshift lamp bulb
- Open or shorted wiring in the lamp circuit
- Faulty PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- 1-4 upshift lamp does not illuminate when skip shift is active
- Transmission may not skip gears as intended
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to verify the code and check for related codes.
Step 2: Visually inspect the 1-4 upshift lamp bulb and replace if burned out.
Step 3: Check wiring and connectors for damage, corrosion, or shorts; repair as needed.
Step 4: If wiring and bulb are good, test the PCM output; replace PCM if faulty.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, it is generally safe to drive, but the skip shift feature may not work properly, and the Check Engine Light will remain on.
How much does it cost to fix?▼
Typically $50-$150, mostly for bulb replacement or wiring repair. PCM replacement is rare and more expensive.