What Does B1813 Mean?
This code indicates the Body Control Module (BCM) has detected a short to ground condition in the backup lamp switch input circuit. The backup lamp switch, typically mounted on the transmission or gear selector, signals when the vehicle is shifted into reverse. The BCM has detected abnormally low voltage (near 0V) on this circuit when it should read battery voltage or an open circuit signal.
Common Causes
45%
Damaged wiring harness or chafed wire causing short to ground between BCM and backup lamp switch
30%
Failed backup lamp switch with internal short to ground
15%
Corroded or damaged connector at backup lamp switch causing ground contact
10%
BCM internal fault causing false detection of short to ground condition
Diagnostic Steps
1
Step 1: Perform visual inspection of backup lamp switch connector and wiring harness from transmission to BCM, looking for damaged insulation, pinched wires, corrosion, or signs of contact with ground points
2
Step 2: Disconnect backup lamp switch connector and measure resistance between the switch input circuit wire (BCM side) and chassis ground using a digital multimeter - should read open circuit (OL or infinite resistance); if reading low resistance (under 10 ohms), circuit is shorted to ground
3
Step 3: If circuit shows short to ground, inspect wiring along entire run from BCM to switch connector, wiggle test harness while monitoring resistance to locate intermittent short point; check near transmission mount points and areas where harness passes through firewall or body panels
4
Step 4: If wiring tests good, reconnect harness and test backup lamp switch by measuring resistance across switch terminals with transmission in Park/Neutral (should be open circuit) and in Reverse (should be low resistance/continuity)
5
Step 5: If switch tests faulty, replace backup lamp switch; if switch tests good but code persists, suspect BCM internal fault and verify BCM ground connections are clean and tight before considering BCM replacement
6
Step 6: Clear codes, cycle ignition, shift through all gear positions including reverse multiple times, and verify backup lamps operate correctly and code does not return
Estimated Repair Cost
$75 - $400
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a short to ground condition in the backup lamp switch input circuit. The backup lamp switch, typically mounted on the transmission or gear selector, signals when the vehicle is shifted into reverse. The BCM has detected abnormally low vo...
The most common cause of B1813 (Lamp Backup Switch Input Circuit Short To Ground) is: Damaged wiring harness or chafed wire causing short to ground between BCM and backup lamp switch
Typical repair costs for B1813 range from $75 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but backup lamps may not function properly, which creates a safety hazard when reversing as other drivers and pedestrians cannot see reverse intent. Repair promptly to maintain proper lighting function and avoid potential accidents or traffic citations.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1813 to identify the root cause.
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Quick Info
Category
Body
System
Lighting System / Body Electrical
Difficulty
Type
Manufacturer
Recommended Tools
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