B0240: Headlamp Switch Circuit
The body control module has detected an implausible state at the headlamp switch — for example simultaneous low and high beam request, or no signal at all. Lighting functions may be erratic.
What B0240 means
B0240 is a generic OBD-II body code in the lighting group. In plain English: the computer found an electrical fault in that circuit: an open, short or bad connection, or a failed component.
- Check engine light
- Usually off
- Emissions-related
- No
- Limp mode possible
- Not typical
- Drive cycle to clear
- Not required
Get it fixed
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Symptoms
- Warning light or symbol related to the affected system
- Comfort or safety function impaired
Common causes
- 01Headlamp switch worn or failedMost likely
- 02Wiring or connector faultPossible
Can I drive with B0240?
Generally yes.
This fault is unlikely to affect how the car drives. Fix it when convenient to restore the affected feature.
Why we rate it low
- Does not normally turn on the check engine light
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose B0240
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just B0240. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for B0800. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Test the circuit
Inspect the wiring and connector at the headlamp switch and body control module for damage, corrosion or chafing. With a multimeter, check supply voltage, ground and signal against the specifications in the service manual for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Headlamp switch worn or failed; wiring or connector fault. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
B0240 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Moderate
- Good DIY job?
- Yes, with a scan tool
Needs a scan tool and some experience with testing.
Parts and systems involved
- Headlamp switch
- Body control module
B0240 FAQ
What does B0240 mean?
B0240 means “Headlamp Switch Circuit”. The body control module has detected an implausible state at the headlamp switch — for example simultaneous low and high beam request, or no signal at all. Lighting functions may be erratic.
Is B0240 serious? Can I keep driving?
We rate B0240 as low severity. Generally yes. This fault is unlikely to affect how the car drives. Fix it when convenient to restore the affected feature.
What causes B0240?
The most common causes, from most to least likely: Headlamp switch worn or failed; Wiring or connector fault. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix B0240?
Typical labor is about $65–$250 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix B0240 myself?
DIY difficulty is moderate. Many owners can handle it with a scan tool, a multimeter and basic hand tools. Always confirm the cause before buying parts.
Will B0240 clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.