Accessory Delay Relay Coil Circuit Short To Battery
The accessory delay relay coil is receiving constant power directly from the battery instead of being controlled properly by the ECU. It's like a light switch that's stuck in the "on" position because the wire is shorted directly to power.
The ECU monitors the voltage and current flowing through the accessory delay relay coil circuit. Under normal conditions, the coil receives controlled voltage pulses from the ECU. When the coil circuit shorts directly to battery voltage, the ECU detects abnormally high voltage that cannot be controlled, triggering the fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Relay Coil Voltage | 0-12V controlled by ECU | Constant 12V+ uncontrolled |
| Coil Current Draw | 50-200mA pulsed | Continuous high current draw |
Code B1304 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B1304 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.