What Does B2108 Mean?
This code indicates the Body Control Module (BCM) has detected a malfunction in the trunk key cylinder switch circuit. The switch, which detects when a key is inserted and turned in the trunk lock, is either sending an incorrect signal, no signal, or an intermittent signal to the BCM. This fault prevents the BCM from properly registering trunk unlock commands from the key cylinder.
Common Causes
45%
Faulty trunk key cylinder switch assembly with worn or corroded internal contacts
30%
Damaged, corroded, or disconnected wiring harness or connector at trunk key cylinder switch
15%
Water intrusion or corrosion in trunk key cylinder switch causing short circuit or open circuit
10%
Failed Body Control Module (BCM) with faulty input circuit for trunk key cylinder switch
Diagnostic Steps
1
Step 1: Perform visual inspection of the trunk key cylinder switch and its connector for physical damage, corrosion, water intrusion, or loose connections. Check for bent pins or debris in connector.
2
Step 2: Using a multimeter, test the trunk key cylinder switch continuity with key inserted and turned. Verify switch opens and closes properly (typically changes from open to ground when key is turned). Compare readings to manufacturer specifications.
3
Step 3: Check voltage supply and ground at the switch connector using a multimeter. Verify battery voltage on supply wire and clean ground on ground wire with ignition on.
4
Step 4: Inspect wiring harness from trunk key cylinder switch to BCM for chafing, pinching, or breaks. Pay special attention to areas where trunk lid flexes and harness passes through trunk hinges or rubber grommets.
5
Step 5: If switch and wiring test good, perform BCM input circuit test by backprobing the BCM connector and simulating switch operation while monitoring BCM response with scan tool live data.
6
Step 6: Clear the code, operate the trunk key cylinder multiple times, and verify repair by checking for code return and proper trunk unlock function.
Estimated Repair Cost
$75 - $400
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a malfunction in the trunk key cylinder switch circuit. The switch, which detects when a key is inserted and turned in the trunk lock, is either sending an incorrect signal, no signal, or an intermittent signal to the BCM. This fault pre...
The most common cause of B2108 (Trunk Key Cylinder Switch Failure) is: Faulty trunk key cylinder switch assembly with worn or corroded internal contacts
Typical repair costs for B2108 range from $75 to $400, 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. The primary inconvenience is the inability to unlock the trunk using the key cylinder, though other trunk access methods (remote, interior release) should still function.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2108 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
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