Faulty headlamp switch assembly with worn or dirty internal contacts; Open or chafed wire in the headlamp switch circuit; Corroded or loose electrical connector at the switch or BCM; Blown fuse or faulty relay feeding the headlamp switch circuit; Water intrusion or contamination in the switch or connector; Failed body control module (BCM) input circuit

DTC codes / B08xx · Airbags, seats, doors, lights and comfort systems / B0800

B0800Headlamp Switch Circuit

Q: What does code B0800 mean?

Headlamp Switch Circuit. B0800 is a body control code indicating that the headlamp switch circuit has a fault, such as an open, short, or out-of-range signal. The body control module (BCM) monitors the voltage or resistance on the switch input and sets this code when the reading does not match any valid switch position.

B0800 is a body control code indicating that the headlamp switch circuit has a fault, such as an open, short, or out-of-range signal. The body control module (BCM) monitors the voltage or resistance on the switch input and sets this code when the reading does not match any valid 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 one or more switch positions
Headlamps may stay on constantly regardless of switch position
Parking lamps, tail lamps, or instrument lighting may fail to operate
The headlamp switch may feel loose, stiff, or unresponsive
Often no symptoms besides the warning light if the fault is intermittent

Common causes, most likely first

Faulty headlamp switch assembly with worn or dirty internal contacts
Open or chafed wire in the headlamp switch circuit
Corroded or loose electrical connector at the switch or BCM
Blown fuse or faulty relay feeding the headlamp switch circuit
Water intrusion or contamination in the switch or connector
Failed body control module (BCM) input circuit

How to diagnose and fix it

Check all fuses related to the headlamp switch circuit and replace any blown fuse
Inspect the headlamp switch connector for corrosion, loose pins, or water intrusion and clean or repair as needed
Test the switch with a multimeter for continuity or resistance changes across each position
Backprobe the switch signal wire at the BCM and compare voltage readings with the service manual specifications
Check for opens or shorts in the wiring between the switch and the BCM using a wiring diagram
Replace the headlamp switch if it fails the resistance or continuity test
If the circuit and switch test good, diagnose or replace the BCM as required

What the headlamp switch test misses

A headlamp switch can pass a basic continuity test yet still set B0800 because the BCM expects a specific voltage divider signal that only fails under load or temperature change.
Corrosion inside the switch connector is a common cause that looks like a failed switch, so always inspect the pins before condemning the switch.
B0800 can be set by a weak or failing battery because low voltage during cranking can make the BCM misread the switch input.
Aftermarket LED or HID headlamp conversions can alter circuit resistance and trigger this code even when the factory switch is healthy.
The BCM may store B0800 intermittently if the switch is left between detents, so verify the switch clicks firmly into each position.

Can I keep driving with B0800?

You can usually drive during daylight, but avoid driving at night or in low-visibility conditions until the fault is repaired, because the headlamps may not operate correctly. If the headlamps stay on constantly, disconnect the battery when parked to prevent drain.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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