What Does B2104 Mean?
This code indicates the Body Control Module (BCM) has detected a malfunction in the passenger door key cylinder switch circuit. The key cylinder switch monitors whether a physical key is inserted and turned in the passenger door lock. The BCM detected either no signal, an incorrect signal, or an intermittent signal from this switch when it should be operational.
Common Causes
45%
Faulty or corroded key cylinder switch contacts or internal switch mechanism failure
30%
Damaged, corroded, or disconnected wiring harness between door jamb and BCM
15%
Water intrusion or corrosion in key cylinder switch connector terminals
10%
BCM internal circuit fault or software corruption
Diagnostic Steps
1
Step 1: Perform visual inspection of passenger door key cylinder and switch connector for obvious damage, corrosion, water intrusion, or loose connections. Check door harness routing through door jamb for pinching or fraying.
2
Step 2: Using a digital multimeter, backprobe the key cylinder switch connector and measure resistance across switch terminals while turning the key through lock/unlock positions. Expect 0-5 ohms in activated position and infinite resistance (open circuit) in rest position.
3
Step 3: Check for power and ground at the switch connector using multimeter. Verify battery voltage on power supply wire and continuity to ground on ground circuit with ignition on.
4
Step 4: Inspect door jamb wiring harness for breaks or shorts by measuring continuity from switch connector pins to BCM connector pins with connector disconnected. Resistance should be less than 1 ohm for each circuit.
5
Step 5: If all circuits test good, remove key cylinder assembly and bench test the switch mechanism separately with multimeter to isolate internal switch failure from wiring issues.
6
Step 6: Clear codes, reinstall/repair components as needed, and cycle key cylinder through all positions multiple times while monitoring live data on scan tool to verify proper switch operation and confirm no code return.
Estimated Repair Cost
$120 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a malfunction in the passenger door key cylinder switch circuit. The key cylinder switch monitors whether a physical key is inserted and turned in the passenger door lock. The BCM detected either no signal, an incorrect signal, or an int...
The most common cause of B2104 (Door Passenger Key Cylinder Switch Failure) is: Faulty or corroded key cylinder switch contacts or internal switch mechanism failure
Typical repair costs for B2104 range from $120 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this affects only the passive entry function via key cylinder on passenger door. Vehicle security and keyless entry systems may have reduced functionality, but vehicle operation and safety systems are not compromised.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2104 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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