What Does B2721 Mean?
B2721 indicates the Body Control Module (BCM) has detected a fault in the PASS-Key (Passive Anti-Theft System Key) detection circuit. This security system uses a resistor pellet embedded in the ignition key that must match a specific resistance value for the vehicle to start. The BCM has identified either an out-of-range resistance reading, an open or short circuit in the key reading sensor, or a communication failure between the key transponder reader and the control module.
Safety Warning
Vehicle may experience no-start condition or stalling, leaving you stranded. While not immediately dangerous if the vehicle is running, this should be repaired urgently as the security system may prevent starting at any time, creating potential safety risks if immobilized in unsafe locations.
Common Causes
35%
Worn or damaged ignition key resistor pellet causing incorrect resistance reading or intermittent contact
30%
Faulty ignition lock cylinder key sensor contacts or damaged wiring in the steering column
20%
Corroded or loose connector at the BCM or ignition cylinder preventing proper signal transmission
15%
Failed Body Control Module unable to properly read or process the key resistance signal
Diagnostic Steps
1
Step 1: Visually inspect the ignition key for visible damage to the resistor pellet, cracks, or wear. Test the key resistor with a digital multimeter set to ohms by placing probes on both sides of the pellet (typical range 400-11,800 ohms depending on key type). Record the value and verify it remains stable.
2
Step 2: Inspect the ignition lock cylinder key sensor contacts for corrosion, debris, or damage. Check steering column wiring harness for chafing, breaks, or damaged insulation near pivot points.
3
Step 3: Using a digital multimeter, backprobe the key sensor wiring at the BCM connector (engine off, key out) and measure resistance. Compare to manufacturer specifications or expected key resistance value (should match Step 1 reading when key is inserted).
4
Step 4: Check connector terminals at both the BCM and ignition lock cylinder for corrosion, bent pins, or poor contact. Clean connectors with electrical contact cleaner and apply dielectric grease.
5
Step 5: If all wiring and key resistance are within specification, perform BCM voltage supply and ground tests. Verify BCM has proper power (typically 12V) and clean grounds at all connection points.
6
Step 6: After repairs, clear codes, perform key relearn procedure if required, and cycle ignition 10-15 times to verify no-start condition is resolved and code does not return.
Estimated Repair Cost
$75 - $800
Parts + labor, varies by vehicle and location
B2721 indicates the Body Control Module (BCM) has detected a fault in the PASS-Key (Passive Anti-Theft System Key) detection circuit. This security system uses a resistor pellet embedded in the ignition key that must match a specific resistance value for the vehicle to start. The BCM has identified ...
The most common cause of B2721 (PASS-Key Detection Circuit) is: Worn or damaged ignition key resistor pellet causing incorrect resistance reading or intermittent contact
Typical repair costs for B2721 range from $75 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may experience no-start condition or stalling, leaving you stranded. While not immediately dangerous if the vehicle is running, this should be repaired urgently as the security system may prevent starting at any time, creating potential safety risks if immobilized in unsafe locations.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2721 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
Anti-Theft Security System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
