B0100: Exterior Lighting Headlamp Output Circuit Malfunction

What Does B0100 Mean?

Code B0100 indicates that the body control module has detected a fault in the headlamp output circuit. The BCM monitors current flow to the headlamps and has detected an abnormal condition such as an open circuit, short to ground, or overcurrent. This can affect one or both headlamps depending on the specific circuit affected.

Common Causes

• Burned-out headlight bulb
• Corroded headlight connector
• Faulty headlight relay
• Damaged wiring to headlight assembly
• Body control module driver circuit failure

Symptoms

• One or both headlights not working
• Headlight warning message on dashboard
• Headlights flickering
• High beams work but low beams do not or vice versa
• BCM fault code stored

Diagnostic Steps

1. 1Check both headlight bulbs and replace any that are burned out
2. 2Inspect headlight connectors for corrosion or melting
3. 3Test for power and ground at the headlight connector
4. 4Check the headlight relay and fuse
5. 5Measure voltage drop across the headlight circuit
6. 6Test BCM headlight output with a scan tool bi-directional control

Estimated Repair Cost

Frequently Asked Questions