U3004

Code

Generic U — Network/User

Accessory Power Relay

Brand: Generic

Type: U — Network/User

Views: UK: 23 EN: 37 RU: 26

AI status

Completed

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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

Read and record U3004 and any other U-/P-/B-codes from all modules. Note operating state when code set (ignition position, accessory use).
Visually inspect relay, socket, wiring harness and related fuses for obvious damage, corrosion or loose connectors. Repair or replace damaged components.
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.
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.
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.
Check continuity to ground for the relay ground circuit. Repair any poor grounds.
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).
Check for related network communication faults (e.g., U0100, U0121). Address communication issues before replacing modules.
Clear codes, reconnect components, and perform a functional test (operate accessories, cycle ignition). Re-scan and road test to confirm the fault is resolved.
If wiring and relay test good but fault persists, consider BCM/module repair or replacement only after verifying inputs/outputs and network integrity.