B0240 code meaning
Headlamp Switch Circuit
What B0240 means
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.
B0240 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of B0240
- Lights do not follow the switch position or fall back to a fixed setting
- Automatic lights or parking lights cannot be selected
Common causes of B0240
- Most likelyWorn or dirty contacts or resistor track inside the light switch
- PossibleSwitch plug loose or corroded behind the dashboard trim
- Less likelySignal line to the body module shorted to ground or supply
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Headlamp switchBody control module
What each part of B0240 means
| B | Body system: airbags, seat belts, power seats, lights and climate control. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 40 | The exact fault in that area. |
What to do next
- Note B0240 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about B0240
What does B0240 mean?
B0240 means "Headlamp Switch Circuit". Searching J2012 sources turned up no B0240, and no maker applies it to the headlamp switch; the identical title belongs to B0800. It is a generic code, so it means the same on every make.
Is it safe to drive with B0240?
B0240 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will B0240 fail an emissions test?
B0240 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is B0240 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will B0240 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.