What Does B1806 Mean?
This code indicates the Body Control Module (BCM) has detected a fault in the tail lamp output circuit. The BCM monitors the electrical circuit that powers the tail lamps and has identified an abnormal condition such as excessive current draw, insufficient current flow, or an open/short circuit. This is a manufacturer-specific body code that directly affects rear lighting system functionality.
Common Causes
35%
Failed tail lamp bulb(s) causing open circuit or incorrect resistance in the monitored circuit
30%
Corroded or damaged tail lamp socket creating high resistance or intermittent connection
20%
Damaged wiring harness or chafed wires causing short to ground or open circuit between BCM and tail lamps
10%
Failed BCM output driver or internal relay for tail lamp circuit
5%
Poor ground connection at tail lamp assembly or body ground point
Diagnostic Steps
1
Step 1: Perform visual inspection of all tail lamp bulbs with lights activated. Check for burned-out bulbs, incorrect bulb types, or LED assemblies with visible damage. Replace any defective bulbs and retest.
2
Step 2: Inspect tail lamp sockets for corrosion, melted terminals, or moisture intrusion. Remove bulbs and check socket terminals for proper tension and condition. Clean or replace damaged sockets as needed.
3
Step 3: Using a digital multimeter, backprobe the tail lamp connector with lights on and measure voltage at the power supply terminal (should read battery voltage 12-14V). Then measure voltage drop across the circuit from BCM output to lamp socket (should be less than 0.5V).
4
Step 4: Check continuity of the tail lamp circuit wiring from BCM connector to lamp socket with power off. Resistance should be less than 5 ohms. Inspect harness routing for pinch points, chafing, or damage especially near trunk hinges and body seams.
5
Step 5: Verify ground circuit integrity by measuring resistance from lamp ground terminal to battery negative (should be less than 1 ohm). Clean and tighten any corroded ground connections found in the tail lamp area.
6
Step 6: If all wiring and components test good, monitor BCM output at the module connector with a multimeter while commanding tail lamps on via scan tool bidirectional controls. If no voltage present at BCM output, suspect internal BCM failure.
Estimated Repair Cost
$50 - $400
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a fault in the tail lamp output circuit. The BCM monitors the electrical circuit that powers the tail lamps and has identified an abnormal condition such as excessive current draw, insufficient current flow, or an open/short circuit. Thi...
The most common cause of B1806 (Lamp Tail Output Circuit Failure) is: Failed tail lamp bulb(s) causing open circuit or incorrect resistance in the monitored circuit
Typical repair costs for B1806 range from $50 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Driving with inoperative tail lamps is illegal and creates significant safety hazard as following traffic cannot see your vehicle, especially at night or in poor weather. Repair should be completed immediately before operating the vehicle on public roads.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1806 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting System
Difficulty
Type
Manufacturer
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