What Does B1846 Mean?
B1846 indicates the Body Control Module (BCM) has detected an open circuit in the ignition tamper detection system. This security feature monitors the ignition cylinder and lock mechanism for unauthorized access attempts. An open circuit means electrical continuity has been lost between the BCM and the tamper sensor, preventing proper anti-theft system operation.
Common Causes
45%
Damaged or disconnected wiring between BCM and ignition cylinder tamper sensor
30%
Failed ignition cylinder tamper switch or sensor
15%
Corroded or loose connector terminals at ignition cylinder or BCM
10%
Failed Body Control Module internal circuit
Diagnostic Steps
1
Step 1: Perform visual inspection of ignition cylinder area and tamper sensor wiring for obvious damage, disconnected connectors, or signs of previous tampering attempts. Check for aftermarket remote start or security system installations that may have modified factory wiring.
2
Step 2: Locate the ignition tamper sensor connector near the ignition cylinder and disconnect it. Using a digital multimeter, check for continuity through the sensor itself (should show low resistance when intact, infinite resistance if open). Reconnect and verify connector pins are not pushed back or corroded.
3
Step 3: With ignition off, backprobe the tamper sensor circuit at the BCM connector using wiring diagrams to identify correct pins. Measure resistance from BCM connector pin to ignition sensor connector pin - should read less than 5 ohms. If open circuit is found, inspect and repair wiring harness between these points.
4
Step 4: If wiring tests good, monitor live data for ignition tamper sensor status while manipulating ignition cylinder and sensor. An intermittent open condition may indicate internal sensor failure requiring replacement of ignition lock cylinder assembly.
5
Step 5: Clear codes, cycle ignition multiple times, and verify proper tamper sensor operation through live data monitoring. Confirm no additional security-related codes return and anti-theft system functions normally.
Estimated Repair Cost
$125 - $650
Parts + labor, varies by vehicle and location
B1846 indicates the Body Control Module (BCM) has detected an open circuit in the ignition tamper detection system. This security feature monitors the ignition cylinder and lock mechanism for unauthorized access attempts. An open circuit means electrical continuity has been lost between the BCM and ...
The most common cause of B1846 (Ignition Tamper Circuit Open) is: Damaged or disconnected wiring between BCM and ignition cylinder tamper sensor
Typical repair costs for B1846 range from $125 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle remains safe to drive but anti-theft protection is compromised, making it more vulnerable to theft. May also prevent proper starting if BCM enters security lockout mode. Repair within 1-2 weeks to restore full security functionality.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1846 to identify the root cause.
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Quick Info
Category
Body
System
Vehicle Security/Anti-Theft System
Difficulty
Type
Manufacturer
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