Accessory Delay Relay Coil Circuit Open
The accessory delay relay coil isn't receiving proper electrical signal, like a broken switch that can't turn on a light. This prevents the relay from engaging and controlling accessory power circuits.
The ECU monitors voltage and resistance across the accessory delay relay coil circuit. It expects a complete circuit with proper voltage drop when the relay should activate. An open circuit causes no current flow through the coil, preventing the relay from switching on.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Relay coil resistance | 50-150 ohms | Infinite ohms (open circuit) |
| Coil voltage drop | 10-12V when activated | 0V or no voltage detected |
Code B1303 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, B1303 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.