Network, generic (extended)

U3004 Accessory Power Relay

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Spilled liquid corroding a connector in the relay control or feed circuit
Aftermarket device on the diagnostic socket or accessory circuit feeding back voltage
Accessory relay sticking or its coil damaged
Fault in the module that drives the relay

Symptoms

  • 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

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–400
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

accessory power relayrelay wiring

Related codes

U3005U300FU300BU3003

References: static.nhtsa.gov, static.nhtsa.gov, gmupfitter.com.