B1807 Tail Lamp Circuit Open
The Body Control Module (BCM) or Smart Junction Box (SJB) monitors the current on the tail lamp output circuit. When the circuit is commanded on, if the current draw is below the programmed threshold—indicating an open circuit or infinite resistance—the module sets diagnostic trouble code B1807. This fault typically results from a break in the wiring, a blown fuse, a damaged connector, or a failed output driver inside the BCM/SJB.
1. Commonly Affected Makes
2. Most Common Causes
- Open circuit in the wiring between the BCM/SJB and the tail lamps
- Blown fuse in the tail lamp power circuit
- Damaged, loose, or corroded connector terminals at the BCM/SJB or tail lamps
- Internal failure of the output driver in the BCM/SJB
- Blown tail lamp bulbs (on systems that monitor individual bulb load)
3. Symptoms You Will Notice
- Tail lamps inoperative or intermittent
- Check engine or warning light illuminated
- Other lighting circuits may be affected if the BCM/SJB is compromised
4. Step-by-Step Diagnosis
Check for blown fuses in the tail lamp circuit and replace if necessary.
Inspect tail lamp bulbs and replace any that are burned out.
Visually examine wiring and connectors for damage, corrosion, or looseness.
Use a multimeter to test for continuity and voltage at the tail lamp connector with the circuit commanded on.
If all external checks pass, suspect a faulty BCM/SJB output driver and perform module diagnostics.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but driving without functioning tail lamps is illegal and dangerous, especially at night or in low visibility. Have the issue repaired promptly.
How much does it cost to fix?▼
Repair costs range from $50 for a simple fuse or bulb replacement to $500 or more if the BCM/SJB needs replacement and programming.