B1304

Code

Other B — Body

Accessory Delay Relay Coil Circuit Short To Battery

Brand: Other

Type: B — Body

Views: UK: 26 EN: 43 RU: 36

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Page language: EN

Causes

Damaged wiring harness with insulation chafe contacting battery feed
Shorted relay socket or pins to constant battery voltage
Failed accessory-delay relay (internally shorted)
Faulty BCM/auxiliary control module or relay driver transistor stuck on
Corroded or bridged connector terminals
Aftermarket accessory wired incorrectly to a constant 12V feed

Symptoms

Accessory delay function does not turn off or behaves erratically
Accessories remain powered when ignition is off (parasitic drain)
Associated fuse(s) may blow repeatedly
DTC B1304 stored in body/BCM memory
Battery may discharge when vehicle is parked
Intermittent accessory operation or no control of delayed function

What to check

Confirm code presence and freeze frame/occurrence data with scan tool
Visually inspect relay, relay socket, nearby wiring, and connectors for damage or corrosion
Check related fuses for condition and proper rating
Measure battery voltage at relay coil control pin with relay removed and key off/ON
Measure coil resistance across relay coil terminals with known-good relay or service manual value
Perform wiggle test on wiring and connectors while monitoring circuit voltage/scan data

Signal parameters

Expected coil supply when relay energized: approx. battery voltage (~11–14.5 V)
Expected coil control circuit when de-energized: near 0 V or high impedance (no battery voltage present)
Relay coil resistance typical range: ~50–200 Ω (varies by relay; check service data)
Short-to-battery symptom: battery voltage present on coil control circuit when relay should be off

Diagnostic algorithm

Retrieve and record freeze frame, readiness, and related codes. Verify B1304 repeats after clearing and performing the condition test.
Inspect relay and socket: remove accessory-delay relay, visually check socket and wiring for melted plastic, bent pins, corrosion, or bridging to a B+ terminal.
With ignition off, disconnect relay and measure voltage at the control/coil control terminal relative to ground. If battery voltage is present with relay removed and not commanded, suspect a short to B+ or a stuck driver.
Remove relay and test coil resistance across coil pins on the relay itself; compare to specification or swap with a known-good relay of same type.
If voltage is present on the control circuit with relay removed, trace the harness back toward the module. Inspect for chafed spots, pin-to-pin shorts in multi-pin connectors, or terminals contacting a B+ circuit.
Back-probe the control module/BCM output while cycling command (if allowed by service info). Observe whether the module is trying to drive the coil and whether the output is shorted to battery regardless of command.
Isolate sections of wiring by disconnecting connectors and re-checking voltage to localize the short. Repair damaged wiring, replace corroded connectors or relay socket as needed.
If wiring and relay socket are good, suspect internal BCM/driver failure. Confirm with module bench test or replacement per manufacturer procedures.
After repair, clear codes and verify proper operation through multiple cycles and a key-off dwell period to confirm no parasitic feed. Re-scan to ensure code does not return.

Likely causes

Wire from relay coil to control module pin shorted to battery feed (pin contact or chafe)
Accessory-delay relay internally shorted or welded contacts
Relay socket pins contacting constant B+ due to corrosion or bent terminal
BCM/relay driver output shorted internally
Improper aftermarket modification tying coil control circuit to battery

Fault status

⚠️ Status

Accessory delay relay coil circuit has detected a short to battery voltage. The condition may cause the accessory delay function to remain powered or blow fuses and will set a stored diagnostic trouble code.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours