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Home / DTC / U3004 — Accessory Power Relay

U3004 — Accessory Power Relay

Detailed page for trouble code U3004.

33,912codes
59brands
11,451generic
22,461specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
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Code

U3004

HYUNDAI U — Network/User

Accessory Power Relay

Brand: HYUNDAI
Type: U — Network/User
Views: UK: 18 EN: 28 RU: 22
AI status
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Page language: EN

Causes

  • Failed accessory power relay (stuck, burned contacts, open coil)
  • Blown or corroded fuse(s) feeding the relay or accessory circuits
  • Open, shorted or corroded wiring or connectors in the relay control or power circuits
  • Poor ground at relay or BCM
  • Faulty Body Control Module (BCM) or related control module
  • Poor ignition switch or ACC input signal

Symptoms

  • Accessories (radio, power outlets, some body circuits) do not power in ACC/ON
  • Intermittent accessory operation or accessories drop out when key is in ACC/ON
  • No audible click when accessory relay is commanded
  • Battery drain if relay contacts are stuck closed
  • Malfunction Indicator Lamp (MIL) or instrument cluster warning for network/module fault

What to check

  • Read and record U3004 and any related DTCs and freeze frame data with a capable scan tool
  • Verify battery voltage and health before testing (battery fully charged)
  • Visual inspection of accessory power relay, socket, fuses and wiring for corrosion, heat damage, loose pins
  • Check accessory fuses and fusible links for continuity and good contact
  • Swap the accessory relay with a known-good identical relay (if available) to test operation
  • Backprobe relay socket: verify constant battery feed at the relay power terminal and proper ground

Signal parameters

  • Battery feed to relay power terminal: ~12 V (engine off) / ~13.5–14.6 V (engine running)
  • Relay control/coil terminal: ~0 V (inactive) and near battery voltage when BCM energizes the relay or toggles to ground depending on vehicle design
  • Coil continuity: low ohms (manufacturer spec varies) — should not be open or short to chassis
  • When commanded ON, voltage should be present at accessory output terminal (switched battery) to downstream accessories
  • No unexpected high resistance between relay power terminal and battery positive

Diagnostic algorithm

  1. Connect scan tool, record code(s) and attempt to reproduce the fault with accessory/AUX/ACC ON.
  2. Verify battery voltage and charge as required. Low supply can produce false results.
  3. Inspect relay, relay socket, fuses and wiring for damage or corrosion. Repair obvious problems.
  4. With ignition OFF remove relay and inspect pins for corrosion or overheating. Replace relay if doubtful.
  5. With a multimeter backprobe the relay socket: verify constant battery at the feed terminal and ground continuity at ground terminal.
  6. Command ACC/Accessory ON (or use scan tool to energize relay) and measure control voltage at the relay coil terminal. If control signal present but relay doesn’t operate, replace relay.
  7. If control signal is absent, trace control wire back to the BCM: check connector pins, continuity to module and for short to ground or battery.
  8. Check for related communication DTCs (CAN bus) and verify BCM is powered and communicating. Repair/replace/flash BCM only after wiring and relay are confirmed good.
  9. After repairs, clear codes and perform a function test and road/test cycle to verify fault does not return.
  10. If intermittent or complex network faults remain, consult Hyundai service information or technical service bulletins for module programming or known issues.

Likely causes

  • Defective accessory power relay
  • Blown fuse or poor fuse contact
  • Wiring harness damage or connector corrosion at relay socket
  • Faulty BCM output or module communication error

Fault status

⚠️ Status
Accessory Power Relay control fault — the body control module reported incorrect or missing control/feedback for the accessory power relay. Accessories may not receive switched power.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

U3000 U3001 U3002 U3003 U3005 U0100
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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