What Does B1559 Mean?
This code indicates the Body Control Module (BCM) has detected an electrical fault in the door lock cylinder circuit. The BCM monitors the door lock cylinder switch signal to detect key-based lock/unlock operations and has identified an open circuit, short circuit, or resistance issue outside normal parameters. This affects the vehicle's passive entry and security systems, preventing proper recognition of physical key operation in the door lock cylinder.
Common Causes
40%
Damaged or corroded wiring harness and connectors between door lock cylinder switch and BCM
30%
Failed door lock cylinder switch or internal switch mechanism
20%
Water intrusion or corrosion at door lock cylinder switch causing internal short or open circuit
10%
Faulty Body Control Module (BCM) with internal circuit failure
Diagnostic Steps
1
Step 1: Perform visual inspection of door lock cylinder and surrounding area for physical damage, water intrusion, or corrosion. Remove door panel to access lock cylinder wiring and connectors.
2
Step 2: Using a digital multimeter, test continuity and resistance of the door lock cylinder switch by operating the key in the lock cylinder while measuring across the switch terminals (typical resistance should be less than 5 ohms closed, infinite open).
3
Step 3: Inspect and test wiring harness from door lock cylinder switch to BCM for opens, shorts to ground, or shorts to power using multimeter continuity and resistance tests. Pay special attention to flex points where door opens/closes.
4
Step 4: Backprobe the BCM connector at the door lock cylinder circuit pins and verify proper voltage supply (typically 5V or 12V reference) and ground circuit with multimeter while comparing to manufacturer specifications.
5
Step 5: If all circuits test normal, perform BCM voltage monitoring while cycling the lock cylinder to verify signal changes are being transmitted. If no signal change occurs, replace door lock cylinder switch.
6
Step 6: Clear codes, test door lock cylinder operation with key, and verify code does not return. Monitor freeze frame data to confirm proper circuit operation.
Estimated Repair Cost
$150 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an electrical fault in the door lock cylinder circuit. The BCM monitors the door lock cylinder switch signal to detect key-based lock/unlock operations and has identified an open circuit, short circuit, or resistance issue outside normal...
The most common cause of B1559 (Door Lock Cylinder Circuit Failure) is: Damaged or corroded wiring harness and connectors between door lock cylinder switch and BCM
Typical repair costs for B1559 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 as this code does not affect vehicle operation or safety systems. The primary concern is inconvenience as key-based door lock/unlock functions may not work properly and security features may be compromised, but repair can be scheduled at convenience.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1559 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Body
System
Body Control and Security System
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
