Lamp Turn Signal Rear Output Circuit Failure
The rear turn signal lamp circuit isn't working properly—the car's computer detected an electrical problem similar to a light switch that won't turn on or off correctly. This means the rear turn signal isn't functioning as intended, creating a safety issue.
The body control module monitors the rear turn signal lamp circuit by measuring voltage and current draw when the signal is activated. If the circuit shows an open condition (no current), short to ground, or excessive resistance, the ECU logs this fault. The system expects proper current flow within specific thresholds when the turn signal switch is engaged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Lamp Current Draw | 0.5–3.0 amps (lamp on) | Below 0.1 amps or open circuit |
| Circuit Voltage | 11–14 volts (lamp active) | 0 volts or shorted to ground |
Code B1802 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, B1802 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.