What Does B1872 Mean?
This code indicates that the Body Control Module (BCM) has detected an unintended voltage supply on the turn signal/hazard lamp power feed circuit. The circuit is receiving battery voltage when it should not be energized, suggesting a short to power condition. This fault affects the vehicle's external lighting signaling system and prevents proper control of turn signals and hazard flashers.
Common Causes
40%
Damaged or chafed wiring harness causing short to B+ in turn signal/hazard circuit between BCM and multifunction switch
30%
Failed multifunction switch with internal short to battery voltage
20%
Corroded or moisture-contaminated connector terminals causing cross-circuit voltage bleed
10%
Faulty BCM with internal circuit failure or aftermarket lighting installation causing backfeed
Diagnostic Steps
1
Step 1: Perform visual inspection of turn signal/hazard wiring harness from BCM through steering column to multifunction switch, checking for pinched, chafed, or damaged insulation that could contact B+ sources. Pay special attention to areas where harness passes through firewall and steering column.
2
Step 2: Disconnect BCM connector and use multimeter to measure voltage on turn signal power feed circuit terminal (consult wiring diagram for specific pin). Should read 0V with ignition on and switch unactivated. If battery voltage present, short exists between BCM and switch.
3
Step 3: Disconnect multifunction switch connector and recheck voltage at BCM-side of circuit. If voltage disappears, switch is faulty. If voltage remains, short exists in harness between BCM and switch connector.
4
Step 4: Inspect all turn signal/hazard lamp sockets and bulbs for damage, improper bulb installation, or moisture intrusion that could cause backfeed through adjacent circuits.
5
Step 5: Check for aftermarket accessories (trailer wiring, LED conversions, alarm systems) that may have been improperly tapped into turn signal circuit causing voltage backfeed.
6
Step 6: After repairs, clear codes, cycle turn signals and hazards through all positions, then verify code does not return and all lighting functions operate normally.
Estimated Repair Cost
$100 - $650
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected an unintended voltage supply on the turn signal/hazard lamp power feed circuit. The circuit is receiving battery voltage when it should not be energized, suggesting a short to power condition. This fault affects the vehicle's extern...
The most common cause of B1872 (Turn Signal / Hazard Power Feed Circuit Short To Battery) is: Damaged or chafed wiring harness causing short to B+ in turn signal/hazard circuit between BCM and multifunction switch
Typical repair costs for B1872 range from $100 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may be drivable but turn signals and hazard lights may not function properly, significantly reducing ability to communicate lane changes and emergency stops to other drivers. Repair should be completed promptly as this is a critical safety system required by law.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1872 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Exterior Lighting
Difficulty
Type
Manufacturer
Recommended Tools
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