What Does B2403 Mean?
This code indicates that the Body Control Module (BCM) has detected an electrical fault in the front fog lamp switch circuit. The BCM monitors the switch input signal and has identified either an open circuit, short circuit, high resistance, or incorrect voltage reading when the switch is activated or at rest. This affects the vehicle's auxiliary lighting system and prevents proper operation of the front fog lamps.
Common Causes
45%
Faulty fog lamp switch with internal contact wear, corrosion, or mechanical failure
30%
Damaged wiring harness or corroded connectors between switch and BCM
15%
Poor ground connection at fog lamp switch circuit or BCM ground
10%
Failed Body Control Module (BCM) with internal circuit board damage
Diagnostic Steps
1
Step 1: Perform visual inspection of fog lamp switch for physical damage, loose mounting, or signs of moisture intrusion. Check switch connector for corrosion, bent pins, or loose connection.
2
Step 2: Using a digital multimeter, test fog lamp switch continuity by disconnecting the switch connector and measuring resistance across switch terminals in both ON and OFF positions. Expected readings: infinite resistance when OFF, near-zero ohms when ON.
3
Step 3: With switch disconnected, check voltage supply at switch harness connector using multimeter. Should read battery voltage (12-14V) on power supply wire with ignition ON. Verify ground circuit shows less than 0.5 ohms resistance to chassis ground.
4
Step 4: Inspect wiring harness from switch to BCM for chafing, pinching, or damage. Pay special attention to areas where harness passes through firewall or flex points. Use wiggle test while monitoring circuit voltage to identify intermittent opens or shorts.
5
Step 5: If all wiring and switch test good, check BCM connector terminals for corrosion or terminal spread. Verify BCM ground connections are clean and tight with less than 0.1 ohms resistance to chassis ground.
6
Step 6: Clear codes, cycle fog lamp switch multiple times, and retest. If code returns immediately with known-good switch and wiring, BCM replacement may be necessary. Verify repair by operating fog lamps through multiple cycles without code reoccurrence.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected an electrical fault in the front fog lamp switch circuit. The BCM monitors the switch input signal and has identified either an open circuit, short circuit, high resistance, or incorrect voltage reading when the switch is activated ...
The most common cause of B2403 (Front Fog Lamp Switch Circuit) is: Faulty fog lamp switch with internal contact wear, corrosion, or mechanical failure
Typical repair costs for B2403 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This code does not affect vehicle safety or driveability and the vehicle is safe to operate normally. Fog lamps are auxiliary lighting for poor weather conditions, so repair can be scheduled at convenience unless required by local regulations or frequently driving in fog.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2403 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System (Auxiliary Lighting)
Difficulty
Type
Generic (SAE)
Recommended Tools
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