Wiper Rear Motor Up Relay Coil Circuit Short To Battery
The rear wiper motor's relay coil is receiving too much voltage directly from the battery instead of being properly controlled. Think of it like a light switch that's stuck on because someone wired it backwards to the power source.
The ECU monitors the voltage and current through the rear wiper relay coil circuit. It expects a controlled voltage signal to activate the relay, but detects an uncontrolled short directly to battery voltage. When battery voltage is present on the coil when it shouldn't be, the ECU flags this as a short-to-battery condition.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Relay Coil Voltage | 0V (off) or 12V (on) when controlled | Continuous 12V+ when relay should be off |
| Relay Coil Current | 0-500mA during normal operation | >500mA or constant draw indicating short |
Code B1820 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, B1820 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.