B0240Headlamp Switch Circuit
- Generic OBD-II code · Body
- How the car detects it
- Searching J2012 sources turned up no B0240, and no maker applies it to the headlamp switch; the identical title belongs to B0800. Saab gives the number another job: in the 9-3 climate system B0240 06 means the defrost door motor circuit is open or grounded, with wrong air distribution as a result, and B0241 01 that this motor is shorted to B+. Going by its title, the code concerns the light switch input. Modern switches rarely carry lamp current. In US7230350B2 a series resistor chain gives each position (Auto, Off, Park, Headlamp) its own voltage band, read by an 8-bit converter, and the bands stay clear of 0 and 255 so a grounded line or one shorted to battery lands outside all of them. US8125101B1 then falls back to the mode closest to the driver's choice.
- What you may notice
- Lights do not follow the switch position or fall back to a fixed setting
- Automatic lights or parking lights cannot be selected
- Likely causes
- LikelyWorn or dirty contacts or resistor track inside the light switch
- PossibleSwitch plug loose or corroded behind the dashboard trim
- RareSignal line to the body module shorted to ground or supply
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.