Body, generic

B0240 Headlamp Switch Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Worn or dirty contacts or resistor track inside the light switch
Switch plug loose or corroded behind the dashboard trim
Signal line to the body module shorted to ground or supply

Symptoms

  • Lights do not follow the switch position or fall back to a fixed setting
  • Automatic lights or parking lights cannot be selected

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–400
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

headlamp switchbody control module

Related codes

B0800B0228B0278

References: saabwisonline.com, patents.google.com, patents.google.com.