P0804 — Upshift/Skip Shift Lamp Control Circuit #

Note: The exact wording of this DTC may differ depending on the vehicle manufacturer. Consult your OEM (Original Equipment Manufacturer) service literature for precise terminology.
Known label variations:

• Upshift Lamp Control Circuit (Chrysler, GM)
• Skip Shift Indicator Lamp Circuit (GM, Dodge)
• Shift Light Control Circuit (Ford, some European OEMs)
• Gear Shift Lamp Control Circuit (BMW, Mercedes-Benz)

Summary of Code P0804 #

P0804 is an OBD-II (On-Board Diagnostics II) trouble code indicating a problem with the circuit that controls the upshift or skip shift indicator lamp on the dashboard. This indicator lamp is designed to prompt the driver when to change gears, primarily for fuel efficiency or emission reasons. The code is set when the Powertrain Control Module (PCM) or Transmission Control Module (TCM) detects an electrical fault—such as an open, short, or unexpected voltage—in the lamp control circuit. While this code does not directly affect drivability, it signals a failure in the system that supports optimal shifting behavior. The seriousness varies depending on whether the lamp is stuck on, off, or flickering.

Common Symptoms for Code P0804 #

A vehicle with a stored P0804 code may present subtle or no noticeable drivability issues, but the following symptoms are frequently observed:

• Upshift or skip shift lamp does not illuminate when it should
• Indicator lamp stays on constantly
• Intermittent illumination or flickering of the shift lamp
• Shift recommendations not being displayed
• Possible minor fuel economy decrease (if the driver misses optimal shift points)
• Stored Check Engine Light (CEL) or Service Engine Soon lamp

Probable Causes for Code P0804 #

The most common sources of P0804 are electrical in nature. Based on frequency, here’s what typically triggers this DTC:

1. Failed upshift/skip shift indicator bulb or LED
2. Open or shorted wiring in the lamp control circuit
3. Corroded or loose connector at the lamp or control module
4. Faulty shift indicator lamp driver in PCM/TCM
5. Faulty instrument cluster (rare)

Step-by-Step Diagnosis for Code P0804 #

Systematically diagnosing a P0804 code ensures you don’t overlook simple faults. Follow these steps:

• Read all stored and pending DTCs with a scan tool and note freeze-frame data.
• Use the scan tool to test lamp activation (if supported by OEM software).
• Visually inspect the upshift/skip shift lamp in the cluster for operation during key-on, engine-off (KOEO) self-check.
• Check the relevant fuses for the instrument cluster and lamp circuits.
• Inspect wiring and connectors between the PCM/TCM and the indicator lamp for signs of damage, corrosion, or loose pins.
• Test the lamp with a multimeter (voltage and continuity checks) to verify functionality.
• Check for proper ground at the lamp and module connector.
• If all wiring and lamp test good, perform control module output tests (may require OEM scan tool).
• Consult OEM wiring diagrams and service bulletins for known issues or recalls.

Possible Repairs for Code P0804 #

Remedies for P0804 depend on the identified cause. Typical repairs include:

• Replace faulty upshift/skip shift indicator bulb or LED
• Repair or replace damaged wiring/connectors in the lamp circuit
• Clean corroded terminals and ensure secure connector fitment
• Replace blown fuse(s) related to the instrument cluster or indicator lamp circuit
• Reprogram or replace PCM/TCM if internal lamp driver has failed (rare and typically verified last)
• Replace instrument cluster if internal fault is confirmed (uncommon)

Is It Safe to Drive With Code P0804? #

Yes – with limitations. The P0804 code itself does not pose a direct risk to vehicle operation, safety, or emissions. However, if the upshift/skip shift lamp is nonfunctional, you may miss optimal shift points—potentially affecting fuel economy and emission performance. If the check engine light is on, ensure no other codes are present that could impact safety or drivability. In rare cases, if the lamp circuit shares power or ground with other vital systems, further investigation should be prioritized.

Vehicles Most Commonly Affected by Code P0804 #

This DTC is seen most frequently on vehicles equipped with manual transmissions and skip shift features, especially those designed to meet specific emission or fuel efficiency regulations. Vehicles commonly affected include:

• Chevrolet Camaro (manual transmission, skip shift feature)
• Dodge Challenger and Charger (manual transmission)
• Ford Mustang (manual transmission, shift light models)
• BMW 3 Series (manual models, shift indicator equipped)
• Chevrolet Corvette (C5, C6 generations with skip shift)
• Some Mercedes-Benz manual transmission models

Common Mistakes & Best Practices for Code P0804 #

Missteps often occur when technicians overlook basic checks or replace expensive components prematurely. Avoid these pitfalls:

• Neglecting to check the bulb/LED first – It’s the most common failure point.
• Overlooking simple fuse or connector issues.
• Failing to inspect wiring for intermittent faults or chafing.
• Replacing the PCM/TCM or instrument cluster without confirming the true source of the failure.
• Not consulting OEM wiring diagrams or known service bulletins.

Express FAQ for Code P0804 #

Q: Will this code cause my vehicle to fail emissions testing?
A: Not directly. P0804 is not an emissions-critical code, but an illuminated check engine light may cause automatic failure in some states or regions.

Q: Can I reset the code and ignore the lamp issue?
A: You can clear the code, but if the underlying problem is not fixed, the code will return. It’s best to address the root cause to ensure optimal vehicle operation.