Fault code B1800 – a step-by-step guide to diagnosing and fixing it

Error code B1800 is displayed and the check engine light is on - what does this mean?

The DTC B1800 is a manufacturer-specific fault code that is recognized by the OBD system and typically indicates a problem with the vehicle lighting or electrical components. This code is usually interpreted differently for different vehicle brands and can relate to headlights, tail lights or other lighting systems.

What causes can this error code have?

• Defective bulbs in headlights or tail lights
• Damaged wiring in the lighting system
• Corroded or loose plug connections
• Defective light switch or relay
• Problems with the body control module (BCM)
• Short circuit in the electrical system
• Defective fuses in the lighting circuit
• Faulty earth connections

What symptoms occur in parallel with fault code B1800?

• Lighting problems: Headlights or tail lights do not work properly
• Intermittent lighting: Lights flicker or fail sporadically
• Warning lights: Indicator lights for lighting illuminate in the dashboard
• Electrical faults: Other electrical systems may be affected
• No response to light switch: Lights cannot be switched on or off

How to fix the problem of trouble code B1800?

• Repairing trouble code B1800 requires a systematic diagnosis of the lighting system.
• Checking and replacing defective bulbs in all lighting units and checking the correct wattage and voltage
• Inspection of the entire cabling for damage, breaks or chafing with subsequent repair or replacement of damaged cables
• Cleaning and securing all plug connections in the lighting system and applying contact spray in the event of corrosion
• Replacement of the light switch or defective relays after prior functional testing with a multimeter
• Diagnosis and, if necessary, reprogramming or replacement of the body control module by a specialist workshop
• Checking and replacing blown fuses and checking for short circuits in the system