B0800Headlamp Switch Circuit
- Generic OBD-II code · Body
- How the car detects it
- B0800 lacks any public evidence; no J2012 extract or service document mentions it. The title concerns the light switch that tells the body control module which lamps to energise. In the GM-developed Saab 9-3 the BCM checks switch positions 1 and 2 and logs B2585 05 or B2575 05 when the respective line rises above 10.2 V; dipped beam then stays on whatever the switch says. GM's 2011 Saab 9-5 compares its headlamp-on and headlamp-off inputs, stores B257A on an implausible combination and falls back to automatic headlamp control. FMVSS 108 requires every car to have a dipper switch and a high-beam telltale. Both fallbacks keep the lights usable, so the fault mostly shows as lost manual control rather than darkness.
- What you may notice
- Dipped beam stays on regardless of switch position
- Lights only work in automatic mode
- Parking lights cannot be selected separately
- Likely causes
- LikelyWorn or corroded contacts in the light switch
- PossibleSwitch signal wire shorted to battery voltage
- PossibleLoose or damaged plug behind the switch
- RareSwitch input of the body control module faulty
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.