Faulty headlamp switch assembly (worn contacts or internal failure); Open or shorted wiring in the headlamp switch circuit; Corroded or loose electrical connector at the switch or BCM; Blown fuse or poor ground connection for the headlamp circuit; Failed body control module (BCM) input driver; Aftermarket accessories tapped into the headlamp circuit causing voltage irregularities

DTC codes / B02xx · Airbags, seats, doors, lights and comfort systems / B0240

B0240Headlamp Switch Circuit

Q: What does code B0240 mean?

Headlamp Switch Circuit. B0240 indicates that the body control module (BCM) has detected an abnormal condition in the headlamp switch circuit, which includes the switch itself, its wiring, and the BCM input. The BCM monitors voltage or resistance on the circuit and sets this code when the signal is outside the expected range for the current switch position.

B0240 indicates that the body control module (BCM) has detected an abnormal condition in the headlamp switch circuit, which includes the switch itself, its wiring, and the BCM input. The BCM monitors voltage or resistance on the circuit and sets this code when the signal is outside the expected range for the current switch position.

SystemBody

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaAirbags, seats, doors, lights and comfort systems

Symptoms you may notice

Headlamps may not turn on in any switch position
Headlamps may stay on continuously regardless of switch position
Parking lamps, tail lamps, or instrument cluster lighting may fail to illuminate
Intermittent headlamp operation when the switch is jiggled or in certain positions
Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

Faulty headlamp switch assembly (worn contacts or internal failure)
Open or shorted wiring in the headlamp switch circuit
Corroded or loose electrical connector at the switch or BCM
Blown fuse or poor ground connection for the headlamp circuit
Failed body control module (BCM) input driver
Aftermarket accessories tapped into the headlamp circuit causing voltage irregularities

How to diagnose and fix it

Verify the complaint and check for any related technical service bulletins (TSBs) for the vehicle
Inspect the headlamp switch connector and wiring for corrosion, damage, or loose pins
Test the headlamp switch with a multimeter to confirm it opens and closes circuits correctly in each position
Check fuses and grounds associated with the headlamp circuit
Backprobe the BCM connector to measure voltage or resistance on the headlamp switch input while operating the switch
If the switch and wiring test good, substitute a known-good BCM or perform a relearn procedure as required
Clear the code and verify the repair by operating the headlamp switch through all positions and confirming the code does not return

What the headlamp switch code really means

A B0240 can be set by a simple blown fuse that powers the headlamp switch, so always check fuses before condemning the switch or BCM.
The BCM often monitors the headlamp switch through a resistor ladder; a poor ground at the switch can mimic a failed switch and set this code.
Intermittent B0240 codes are frequently caused by a worn ignition switch or relay that interrupts power to the headlamp circuit, not the headlamp switch itself.
Aftermarket LED or HID headlamp conversions can draw different current and confuse the BCM, leading to a false B0240.
Some vehicles require a BCM relearn or configuration after replacing the headlamp switch, and skipping this step can leave the code stored.

Can I keep driving with B0240?

If the headlamps are working normally, the vehicle is safe to drive during daylight, but avoid driving at night or in low-visibility conditions until the fault is repaired. If the headlamps fail to operate, do not drive the vehicle after dark or in bad weather because you may be difficult to see and unable to see the road clearly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.