What Does B2100 Mean?
This code indicates the Body Control Module (BCM) has detected a malfunction in the driver's door key cylinder switch circuit. This switch signals the BCM when a key is inserted and turned in the door lock cylinder, typically used for theft deterrent disarm and door unlock functions. The BCM has identified an open circuit, short circuit, or incorrect signal from this switch that does not match expected operational parameters.
Common Causes
40%
Faulty or worn key cylinder switch contacts or internal switch mechanism
30%
Damaged, corroded, or disconnected wiring harness between door lock cylinder switch and BCM
20%
Corroded or damaged switch connector terminals at the key cylinder
10%
Failed Body Control Module (BCM) input circuit or internal fault
Diagnostic Steps
1
Step 1: Perform visual inspection of driver's door key cylinder switch connector for corrosion, damage, or moisture intrusion. Check for backed-out pins or loose connections.
2
Step 2: Using a digital multimeter, backprobe the key cylinder switch connector and verify proper voltage supply (typically 5V or 12V reference) from BCM. Measure resistance across switch terminals while manually actuating the key cylinder through lock/unlock positions, expecting continuity changes between open and closed states.
3
Step 3: Inspect the door jamb harness area for pinched, chafed, or broken wires where the harness flexes between door and body. Check continuity from switch connector through to BCM connector on both signal and ground circuits.
4
Step 4: If wiring and voltage supply are confirmed good, remove the key cylinder switch assembly and bench-test with ohmmeter while cycling the mechanism. Replace switch if readings are erratic or show no continuity changes.
5
Step 5: Clear codes, reinstall components, and perform functional test by inserting key and turning lock cylinder in both directions. Monitor live data on scan tool to verify BCM receives proper switch state changes. Re-scan for code reoccurrence.
Estimated Repair Cost
$150 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a malfunction in the driver's door key cylinder switch circuit. This switch signals the BCM when a key is inserted and turned in the door lock cylinder, typically used for theft deterrent disarm and door unlock functions. The BCM has ide...
The most common cause of B2100 (Door Driver Key Cylinder Switch Failure) is: Faulty or worn key cylinder switch contacts or internal switch mechanism
Typical repair costs for B2100 range from $150 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive. This affects only the key-in-door-lock detection function and may prevent proper security system disarm when unlocking with the physical key. Vehicle can still be operated normally using remote key fob or other unlock methods.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2100 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Security System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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