What Does B1845 Mean?
B1845 indicates the Body Control Module (BCM) has detected a fault in the ignition tamper detection circuit. This security system monitors for unauthorized ignition switch manipulation or cylinder tampering attempts. The BCM has identified an abnormal voltage, resistance, or signal pattern in the tamper detection wiring or sensor that indicates either a genuine security breach attempt, a circuit fault, or a failed tamper sensor component.
Common Causes
35%
Damaged or corroded wiring/connectors in the ignition tamper sensor circuit between BCM and ignition cylinder sensor
30%
Failed ignition cylinder tamper detection sensor or switch integrated into the lock cylinder assembly
20%
Previous ignition cylinder service or replacement with incorrect or non-OEM parts causing sensor mismatch
10%
Body Control Module internal fault or corrupted security programming
5%
Actual attempted theft or ignition tampering that triggered legitimate security alert
Diagnostic Steps
1
Step 1: Perform visual inspection of the ignition lock cylinder and surrounding steering column area for signs of forced entry, damage, or previous repair work that may have disturbed tamper sensor wiring
2
Step 2: Using a digital multimeter, test the ignition tamper sensor circuit for continuity and proper resistance values (typically 500-2000 ohms depending on manufacturer) at the BCM connector and ignition cylinder connector with ignition off and key removed
3
Step 3: Monitor live data from the BCM using the scan tool to observe the tamper sensor status in real-time while gently manipulating the ignition cylinder and key - check for intermittent open or short circuit conditions
4
Step 4: Inspect all connectors in the tamper circuit for corrosion, bent pins, or moisture intrusion, paying special attention to the BCM connector and ignition cylinder harness connector behind the steering column
5
Step 5: If wiring and connections test good, remove the ignition lock cylinder assembly and bench-test the integrated tamper sensor with a multimeter to verify proper operation through its full range of motion
6
Step 6: After repairs, clear the code, perform a BCM security system relearn procedure per manufacturer specifications, and verify the tamper circuit operates correctly with multiple key insertions and removal cycles
Estimated Repair Cost
$150 - $650
Parts + labor, varies by vehicle and location
B1845 indicates the Body Control Module (BCM) has detected a fault in the ignition tamper detection circuit. This security system monitors for unauthorized ignition switch manipulation or cylinder tampering attempts. The BCM has identified an abnormal voltage, resistance, or signal pattern in the ta...
The most common cause of B1845 (Ignition Tamper Circuit Failure) is: Damaged or corroded wiring/connectors in the ignition tamper sensor circuit between BCM and ignition cylinder sensor
Typical repair costs for B1845 range from $150 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may still be drivable but security system may be compromised, potentially preventing starting in some cases or leaving the vehicle vulnerable to theft. Some vehicles may enter anti-theft mode and prevent starting until the fault is resolved, requiring immediate repair.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1845 to identify the root cause.
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Quick Info
Category
Body
System
Vehicle Security and Anti-Theft System
Difficulty
Type
Manufacturer
Recommended Tools
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