Wiper Rear Motor Down Relay Coil Circuit Open
The rear wiper relay coil circuit has an open connection, preventing electrical current from reaching the rear wiper motor. Think of it like a broken wire in a circuit—the relay can't activate, so the rear wipers won't work.
The ECU monitors the coil resistance and continuity of the rear wiper relay circuit when the wiper command is activated. It detects if the relay coil cannot be energized due to an open circuit (broken wire, disconnected connector, or failed relay). The fault sets when expected current flow cannot be established through the relay coil.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Relay Coil Resistance | 70-150 ohms | Open circuit (infinite resistance) |
| Relay Coil Current Draw | 0.5-2.0 amps when activated | 0 amps (no continuity) |
Code B1815 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, B1815 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.