U3004 code meaning
Accessory Power Relay
What U3004 means
U3004 concerns the relay, or electronic switch, that feeds the accessory (ACC) circuits once the car is in accessory or run mode. On GM trucks the body module reads the ignition inputs, decides the power mode and energises the matching relays itself. Mazda documents the code in the start stop unit as U3004:17, an ACC relay line above its threshold. Its bulletin SA-023-23 for the 2017–2022 CX-5 traces it to drink spilled near the front cupholder, which corrodes connector C-16: the ignition then cannot be switched off, infotainment stays on and the battery runs flat. Mazda's MT-001/21 lists the same entry among faults caused by aftermarket dongles plugged into the diagnostic connector. The stuck accessory feed matters more to the driver than the code; no MIL.
U3004 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3004
- Ignition or accessory mode cannot be switched off, radio stays on
- Flat battery and no-start after the car has stood
- Accessory functions dead in accessory mode
Common causes of U3004
- Most likelySpilled liquid corroding a connector in the relay control or feed circuit
- PossibleAftermarket device on the diagnostic socket or accessory circuit feeding back voltage
- PossibleAccessory relay sticking or its coil damaged
- Less likelyFault in the module that drives the relay
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Accessory power relayRelay wiring
What each part of U3004 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 04 | The exact fault in that area. |
What to do next
- Note U3004 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U3004
What does U3004 mean?
U3004 means "Accessory Power Relay". U3004 concerns the relay, or electronic switch, that feeds the accessory (ACC) circuits once the car is in accessory or run mode. It is a generic code, so it means the same on every make.
Is it safe to drive with U3004?
U3004 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U3004 fail an emissions test?
U3004 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U3004 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will U3004 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.