What Does B1805 Mean?
This code indicates that the Body Control Module (BCM) has detected a short circuit to ground in the rear turn signal lamp output circuit. The BCM monitors the electrical load on the turn signal circuit and has identified that current is flowing through an unintended path directly to ground, which typically causes the turn signal to not illuminate or blow a fuse. This is a manufacturer-specific body code related to the exterior lighting control system.
Common Causes
40%
Damaged or chafed wiring harness creating a direct ground path between the BCM output and chassis ground
30%
Failed turn signal bulb socket with internal short to ground or corroded socket housing
20%
Defective tail light assembly with internal short circuit or moisture intrusion causing ground fault
10%
Failed Body Control Module with shorted internal output driver circuit
Diagnostic Steps
1
Step 1: Perform visual inspection of the rear turn signal bulbs, sockets, and tail light assemblies for signs of moisture intrusion, corrosion, melted plastic, or physical damage that could cause grounding
2
Step 2: Disconnect the rear turn signal bulb/socket on the affected side and clear the code. If code does not return, the fault is in the bulb socket or tail light assembly. If code returns immediately, proceed to Step 3
3
Step 3: Disconnect the tail light harness connector at the body and measure resistance from the BCM turn signal output wire (at the disconnected connector vehicle side) to chassis ground using a digital multimeter. Reading should be infinite (open circuit); any continuity indicates a wiring harness short
4
Step 4: Inspect the wiring harness routing from the BCM to the rear tail lights, focusing on areas where the harness passes through body panels, near the tailgate/trunk hinge, and underneath the vehicle where chafing or pinching may occur
5
Step 5: If no wiring faults are found, test the turn signal bulb socket by installing a known-good bulb and checking for proper voltage and ground at the socket with turn signal activated using a test light or multimeter
6
Step 6: After repairs, clear codes and operate the turn signals through multiple cycles while monitoring with scan tool to verify the short circuit has been eliminated and proper lamp operation is restored
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected a short circuit to ground in the rear turn signal lamp output circuit. The BCM monitors the electrical load on the turn signal circuit and has identified that current is flowing through an unintended path directly to ground, which t...
The most common cause of B1805 (Lamp Turn Signal Rear Output Circuit Short To Ground) is: Damaged or chafed wiring harness creating a direct ground path between the BCM output and chassis ground
Typical repair costs for B1805 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but turn signal functionality may be impaired, creating a safety hazard for lane changes and turns as other drivers cannot see your intentions. Repair should be completed promptly to maintain safe vehicle operation and comply with traffic laws requiring functional turn signals.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1805 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting System
Difficulty
Type
Manufacturer
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