What Does B1811 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the backup lamp switch input circuit. The backup lamp switch is typically located on the transmission and signals when the vehicle is shifted into reverse gear. An open circuit means the BCM is not receiving the expected electrical signal from the switch, preventing proper operation of the backup lamps and potentially affecting other reverse-related functions like backup camera activation or parking sensors.
Common Causes
35%
Faulty backup lamp switch or internal switch contacts
30%
Open or damaged wiring between BCM and backup lamp switch
20%
Loose, corroded, or damaged connector at backup lamp switch
10%
Damaged wiring harness connector at BCM or poor BCM ground
5%
Faulty Body Control Module
Diagnostic Steps
1
Step 1: Locate the backup lamp switch on the transmission housing and perform a visual inspection of the switch, connector, and wiring for obvious damage, corrosion, or loose connections. Check connector pins for proper seating and signs of moisture intrusion.
2
Step 2: With ignition on and using a digital multimeter, backprobe the backup lamp switch connector to verify voltage supply (typically battery voltage) on the power feed wire. Check wiring diagram for proper pin identification.
3
Step 3: With ignition on, shift transmission into reverse (parking brake applied, wheels chocked) and measure voltage at the backup lamp switch output wire at the connector. Should show battery voltage in reverse, low/no voltage in other gear positions. If no change, switch is likely faulty.
4
Step 4: If switch operates correctly at connector, perform continuity test of the signal wire from backup lamp switch connector to BCM connector using a multimeter with harness disconnected. Resistance should be less than 5 ohms. Check for shorts to ground as well.
5
Step 5: If wiring tests good, connect switch harness and monitor switch input signal at BCM connector while shifting into reverse. If signal is present at BCM but code persists, suspect BCM issue. If signal is absent, replace backup lamp switch.
6
Step 6: After repairs, clear code, cycle ignition, shift through all gears including reverse multiple times, and verify backup lamps operate correctly and code does not return.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an open circuit in the backup lamp switch input circuit. The backup lamp switch is typically located on the transmission and signals when the vehicle is shifted into reverse gear. An open circuit means the BCM is not receiving the expect...
The most common cause of B1811 (Lamp Backup Switch Input Circuit Open) is: Faulty backup lamp switch or internal switch contacts
Typical repair costs for B1811 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but backup lamps will not function, creating a safety hazard when reversing especially at night or in low visibility conditions. This may also violate local vehicle lighting regulations. Repair should be completed promptly to maintain safe operation and legal compliance.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1811 to identify the root cause.
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Quick Info
Category
Body
System
Lighting System / Body Control
Difficulty
Type
Manufacturer
Recommended Tools
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