Wiper Rear Motor Up Relay Coil Circuit Failure
The rear wiper motor's up relay coil isn't working properly, like a broken switch that can't turn on the upward motion. The ECU detected an electrical failure in the relay circuit that controls the rear wiper's upward movement.
The ECU monitors the voltage and current draw of the rear wiper motor up relay coil during activation. It detects shorts, opens, or excessive resistance in the relay circuit by measuring coil voltage drops and current flow. A fault is flagged when the relay fails to energize or shows abnormal electrical resistance.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Relay Coil Voltage | 12V ± 1.5V when energized | Below 10.5V or no voltage detected |
| Coil Current Draw | 0.5A - 1.5A during activation | 0A (open circuit) or excessive draw indicating short |
Code B1818 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, B1818 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.