What does it mean?
B1578 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Lamp Park Input Circuit Short To Ground .
Symptoms
- Parking and tail lamps stay on all the time and cannot be switched off, flattening the battery
- Lights-on warning chime sounds continuously with the door open
- Dash illumination is forced to the dimmed night level in daylight
- Lighting fuse may blow after the circuit has been shorted for a while
- The code sets again immediately after being cleared, without touching the switch
Likely causes
- Park lamp input wire chafed against body metal or a bracket behind the dash
- Water in the headlamp switch or in a kick panel connector pulling the input to ground
- Light switch shorted internally so the park request is permanently active
- Connector terminal bent onto a ground pin
- Loom damaged during a previous dash, radio or aftermarket accessory installation
- Module input stage pulled low internally
- Corroded splice in the lighting circuit where moisture has entered the loom
How to fix it
- Unplug the headlamp switch and see whether the lamps go out and the code stops resetting, which splits switch from harness in one step
- With the switch unplugged, measure resistance from the park input wire to ground; an almost zero value proves the short
- Inspect the loom behind the dash and around the steering column for insulation worn through to bare metal
- Check for water in the switch body and in the kick panel connectors, a frequent cause after a windscreen or heater leak
- Ohm the light switch by itself: no position with the switch off should show continuity to ground
- Repair the shorted section, insulate it and secure it clear of metal edges
- Replace the light switch if it measures shorted internally, and leave the module for last