Body, generic

B0800 Headlamp Switch Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Worn or corroded contacts in the light switch
Switch signal wire shorted to battery voltage
Loose or damaged plug behind the switch
Switch input of the body control module faulty

Symptoms

  • Dipped beam stays on regardless of switch position
  • Lights only work in automatic mode
  • Parking lights cannot be selected separately

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–250
Time0.3–1.5 h

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

Parts involved

headlamp switchbody control module

Related codes

B0240B0810B0811

References: saabwisonline.com, saabwisonline.com, saabwisonline.com, law.cornell.edu.