What Does B1798 Mean?
B1798 indicates the Body Control Module (BCM) has detected a fault in the front turn signal lamp output circuit. This means the BCM is unable to properly control or detect correct operation of one or both front turn signal bulbs, suggesting an open circuit, short to ground, short to power, or excessive resistance in the lighting circuit. The BCM monitors current flow through the turn signal circuit and sets this code when the actual current draw does not match expected parameters.
Common Causes
35%
Burned out or faulty front turn signal bulb causing open circuit or incorrect resistance
30%
Corroded or damaged turn signal bulb socket creating high resistance or poor ground connection
20%
Damaged wiring harness between BCM and front turn signal assembly (chafed, broken, or shorted wires)
10%
Failed Body Control Module output driver circuit for turn signal control
5%
Poor ground connection at turn signal assembly or BCM ground circuit
Diagnostic Steps
1
Step 1: Perform visual inspection of both front turn signal bulbs - remove bulbs and check for burned filaments, physical damage, or incorrect bulb type installed. Inspect sockets for corrosion, melting, or terminal damage.
2
Step 2: Using a digital multimeter, test voltage at the turn signal bulb socket connector with turn signal activated - should read battery voltage (12-14V) on power wire. If no voltage present, check for open circuit in harness between BCM and lamp.
3
Step 3: Test ground circuit at bulb socket using multimeter - measure resistance between ground terminal and known good chassis ground, should be less than 1 ohm. Clean and repair ground connections if resistance is high.
4
Step 4: If power and ground are present, test bulb socket continuity by installing a known-good bulb and activating turn signal. If bulb does not illuminate, replace socket assembly.
5
Step 5: Check wiring harness from BCM to turn signal assembly for chafing, pinching, or damage particularly in areas where harness passes through body panels or near moving components. Repair or replace damaged sections.
6
Step 6: Clear codes and verify repair by activating turn signals and monitoring BCM for proper current draw feedback. Code should not return if circuit is functioning correctly.
Estimated Repair Cost
$50 - $400
Parts + labor, varies by vehicle and location
B1798 indicates the Body Control Module (BCM) has detected a fault in the front turn signal lamp output circuit. This means the BCM is unable to properly control or detect correct operation of one or both front turn signal bulbs, suggesting an open circuit, short to ground, short to power, or excess...
The most common cause of B1798 (Lamp Turn Signal Front Output Circuit Failure) is: Burned out or faulty front turn signal bulb causing open circuit or incorrect resistance
Typical repair costs for B1798 range from $50 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is legal to drive but turn signal functionality may be compromised, creating a significant safety hazard as other drivers cannot anticipate your lane changes or turns. Repair should be completed promptly to maintain safe vehicle operation and avoid traffic citations.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1798 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting System
Difficulty
Type
Manufacturer
Recommended Tools
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