U3004
Accessory Power Relay
Fault on the accessory power relay that switches power to comfort/accessory loads (radio, infotainment, etc.) when the key is in ACC position.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: easy
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
Ordered by how often each turns out to be the cause.
- Relay contacts failed or coil openCommon
- Gateway module routing CAN messages incorrectlyLess likely
- CAN terminating resistor (120 Ω) drifted out of specLess likely
Parts involved
- Accessory Power Relay
- Relay Wiring
U3004 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.