What Does B1799 Mean?
DTC B1799 indicates the Body Control Module (BCM) has detected an open circuit in the front turn signal lamp output circuit. This means the BCM is commanding the turn signal to illuminate but is not detecting current flow through the circuit, suggesting a break in the electrical path between the BCM and the front turn signal bulb. The fault prevents proper turn signal operation on one or both front corners.
Common Causes
45%
Burned out turn signal bulb or poor bulb socket connection with corrosion
30%
Broken or chafed wiring harness between BCM and turn signal assembly
15%
Corroded or loose connector at turn signal assembly or BCM
10%
Failed BCM output driver circuit for turn signal control
Diagnostic Steps
1
Step 1: Perform visual inspection of the front turn signal assemblies. Check for burned out bulbs, inspect socket terminals for corrosion, heat damage, or loose fit. Test bulb continuity with multimeter if visual inspection is inconclusive.
2
Step 2: Inspect the turn signal wiring harness from the lamp assembly back toward the BCM. Look for chafed, pinched, or broken wires, especially in areas where harness passes through body panels or near sharp edges. Check all connectors for corrosion, moisture intrusion, and proper seating.
3
Step 3: Using a multimeter, backprobe the turn signal output wire at the lamp connector while activating the turn signal. Verify voltage is present from the BCM (typically 12V). If voltage is present but bulb doesn't work, issue is at lamp side; if no voltage, trace back toward BCM.
4
Step 4: Disconnect the turn signal connector and measure resistance from the BCM output pin to the lamp connector pin. Reading should be less than 1 ohm. High resistance or infinite reading confirms open circuit in wiring. Also check ground circuit continuity.
5
Step 5: If all wiring and connections test good, suspect BCM internal fault. Test BCM output capability by measuring voltage at BCM connector during turn signal activation. Replace BCM if output driver has failed and all other circuits test normal.
6
Step 6: After repair, clear codes and cycle turn signals multiple times in both directions. Monitor for code return and verify proper flash rate and brightness of all turn signals.
Estimated Repair Cost
$75 - $650
Parts + labor, varies by vehicle and location
DTC B1799 indicates the Body Control Module (BCM) has detected an open circuit in the front turn signal lamp output circuit. This means the BCM is commanding the turn signal to illuminate but is not detecting current flow through the circuit, suggesting a break in the electrical path between the BCM...
The most common cause of B1799 (Lamp Turn Signal Front Output Circuit Open) is: Burned out turn signal bulb or poor bulb socket connection with corrosion
Typical repair costs for B1799 range from $75 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is technically drivable but non-functional turn signals create significant safety hazards for lane changes and turns, increasing accident risk. Repair should be completed immediately as turn signals are legally required safety equipment in all jurisdictions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1799 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting System
Difficulty
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