U3004 Accessory Power Relay Circuit Fault
The U3004 code indicates a fault in the accessory power relay circuit. This relay controls electrical power to the vehicle's accessory systems when the ignition is in the ACC or ON position. The body control module (BCM) or vehicle control unit monitors the relay's status and sets this code when the electrical response does not match the expected command signal. The issue can stem from an open circuit, short to ground, short to battery voltage, or a failed relay itself.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Faulty or damaged accessory power relay
- Open circuit in the relay wiring
- Short to ground in the relay wiring
- Short to battery voltage in the control circuit
- Corroded, loose, or damaged connectors in the relay circuit
- Failed body control module (BCM)
- Blown or incorrect amperage fuse in the power circuit
3. Symptoms You Will Notice
- Accessory systems (radio, power windows, etc.) may not work
- Engine may start but accessories remain inoperative
4. Step-by-Step Diagnosis
Check for blown fuses in the accessory power circuit and replace if necessary
Inspect the accessory power relay for signs of damage or corrosion and test it
Visually inspect wiring and connectors for opens, shorts, or corrosion
Use a multimeter to check for voltage at the relay coil and switch terminals
If all else is good, test the BCM for proper relay control signals
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but some accessories may not work. The vehicle can be driven, but have it diagnosed soon to avoid potential electrical issues.
How much does it cost to fix?▼
Typically $100 to $300, depending on the cause. A relay replacement is cheap, but BCM repair can be more expensive.