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Home / DTC / U3004 — Accessory Power Relay

U3004 — Accessory Power Relay

Detailed page for trouble code U3004.

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Code

U3004

Generic U — Network/User

Accessory Power Relay

Brand: Generic
Type: U — Network/User
Views: UK: 14 EN: 26 RU: 15
AI status
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Page language: EN

Causes

  • Failed or stuck accessory power relay
  • Blown fuse or poor fuse connection on the accessory feed
  • Open, shorted, corroded or disconnected wiring or terminals at the relay socket
  • Bad ground at relay or control module
  • Body control module (BCM) or instrument cluster driver fault
  • Loss of CAN/communication preventing relay control

Symptoms

  • Accessory circuits (radio, cigarette lighter, some dash items) do not power in ACC/ON
  • Accessories drop out or reset intermittently
  • No crank/starting issues if relay also supplies ignition coils in some designs
  • Battery drain or parasitic draw when vehicle is off (if relay stuck closed)
  • Malfunction indicator lamp or communications-related warnings
  • DTC U3004 stored and may be accompanied by other U-codes

What to check

  • Retrieve U3004 and any related codes and freeze-frame data with a scan tool
  • Visually inspect relay, relay socket, fuses and wiring for corrosion, heat damage or loose pins
  • Check accessory fuse(s) for continuity and proper seating
  • Backprobe relay coil and contact terminals; verify battery feed and switched output voltages
  • Verify relay coil control signal from BCM (voltage or ground depending on design) with key in ACC/ON
  • Measure coil resistance and compare with specification; bench-test relay with known good 12V supply

Signal parameters

  • Battery feed at relay common terminal: ~12.0–13.0 V with key ON (measure at relay terminal)
  • Relay coil control: 0 V (inactive) and ~12 V or ground switching (active) depending on vehicle design
  • Relay contact closed voltage: near battery voltage (
  • Relay coil resistance (typical): tens to a few hundred ohms (check service spec for exact value)
  • Contact continuity: near 0 ohms when closed, open (OL) when open
  • Accessory circuit current: varies by accessory — verify against service data; large unexpected current indicates short or overload

Diagnostic algorithm

  1. Read and record U3004 and any other U-/P-/B-codes from all modules. Note operating state when code set (ignition position, accessory use).
  2. Visually inspect relay, socket, wiring harness and related fuses for obvious damage, corrosion or loose connectors. Repair or replace damaged components.
  3. With ignition OFF, remove relay and inspect terminals for corrosion. Bench-test the relay by applying 12 V to the coil and checking contact closure. Replace relay if it fails.
  4. With a DVOM, check for battery voltage at the relay power feed terminal with ignition ON. If missing, trace back to fuse and battery feed circuit.
  5. Backprobe the coil control terminal while commanding ACC/ON. Confirm the BCM provides the expected control (12 V or ground) when the relay should energize. If control is absent, check wiring to BCM and module outputs.
  6. Check continuity to ground for the relay ground circuit. Repair any poor grounds.
  7. If coil control is present but relay does not switch under load, check for excessive current draw on the accessory circuit (disconnect accessory loads one at a time).
  8. Check for related network communication faults (e.g., U0100, U0121). Address communication issues before replacing modules.
  9. Clear codes, reconnect components, and perform a functional test (operate accessories, cycle ignition). Re-scan and road test to confirm the fault is resolved.
  10. If wiring and relay test good but fault persists, consider BCM/module repair or replacement only after verifying inputs/outputs and network integrity.

Likely causes

  • Corroded relay socket or loose connector causing intermittent contact
  • Relay coil not being driven (open coil, damaged driver in BCM)
  • Power feed fuse blown or battery feed wire damaged
  • Accessory load short or excessive current draw preventing relay operation
  • Faulty BCM or other module reporting relay control fault

Fault status

⚠️ Status
Accessory Power Relay fault — control or power feed abnormal (relay not responding, open/short, or module communication failure detected).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

U0100 U0121 U0131 U0155 U0401 U3000
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