Lamp Park Input Circuit Short To Ground
The parking lamp circuit is shorted to ground, meaning electrical current is taking an unintended shortcut instead of flowing through the lamp normally. It's like water escaping through a hole in a pipe instead of reaching the faucet.
The body control module monitors the voltage and resistance of the park lamp input circuit. When a short to ground occurs, the circuit resistance drops abnormally low, causing the voltage to drop below the expected threshold. The ECU detects this condition and sets the fault code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Park Lamp Circuit Voltage | 12V or nominal supply voltage | Below 2V (shorted condition) |
| Circuit Resistance | Hundreds of ohms (normal lamp load) | Near 0 ohms (short to ground) |
Code B1578 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, B1578 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.