1-4 Upshift (Skip Shift) Lamp Control Circuit
Diagnostic trouble code P0804 indicates a malfunction in the control circuit for the 1-4 upshift (skip shift) indicator lamp. The powertrain control module (PCM) sets this code when it detects an improper voltage or resistance level in the circuit responsible for illuminating the skip shift light on the instrument panel.
This code primarily affects the indicator lamp for the skip shift feature and does not typically impact vehicle drivability or safety. It is safe to drive, but should be diagnosed to restore full instrument panel functionality.
Common symptoms
- Illuminated Check Engine Light (MIL)
- 1-4 skip shift indicator lamp fails to illuminate
- 1-4 skip shift indicator lamp stays on constantly
- Skip shift feature may not operate correctly (depending on vehicle design)
- No noticeable drivability issues
Likely causes
- Burned out 1-4 upshift indicator bulb or faulty LED
- Faulty wiring or loose connections in the skip shift lamp circuit
- Corroded or damaged connector at the instrument cluster or PCM
- Faulty skip shift solenoid (if sharing the same circuit)
- Defective instrument cluster
- Failing Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Scan for additional codes and clear the PCM
Look for: Check if P0804 returns immediately or if other transmission/skip shift codes are present, which could indicate a broader circuit issue.
Inspect the 1-4 upshift indicator bulb or LED
Look for: A burned-out bulb or damaged LED in the instrument cluster is a common cause. If the bulb is blown, replacing it may resolve the issue.
Visually inspect the wiring harness and connectors between the PCM and the instrument cluster
Look for: Look for chafed, broken, or melted wires, as well as corroded or loose pins in the connectors that could cause an open or short circuit.
Test the skip shift lamp control circuit for continuity and resistance
Look for: Using a digital multimeter, verify that the resistance in the wiring between the PCM and the lamp matches factory specifications. Infinite resistance indicates an open circuit.
Check the voltage output from the PCM to the lamp circuit
Look for: Command the lamp on using a bidirectional scan tool and measure the voltage at the PCM output pin. If the PCM does not output the correct voltage, the PCM or its programming may be at fault.
This page explains the generic P0804 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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