Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the computer in the car is having trouble matching the transfer case, which helps the car switch between two-wheel and four-wheel drive, with the car's unique ID number.
The vehicle's control module has detected a mismatch between the transfer case and the Vehicle Identification Number (VIN) stored in the system.
The C12B6 code is triggered when the transfer case control module (TCCM) receives a VIN that does not match the VIN stored in the powertrain control module (PCM). This can occur if the transfer case or its module has been replaced with one from another vehicle without proper reprogramming.
• Check engine light or service 4WD light illuminated
• Inability to switch between 2WD and 4WD
• Unusual noises from the transfer case
• Transfer case module replaced with a non-compatible unit
• Incorrect programming or coding of the transfer case module
• Faulty wiring or connections between modules
Transfer Case: A component that transfers power from the transmission to the front and rear axles in a four-wheel-drive vehicle.
VIN: Vehicle Identification Number, a unique code used to identify individual motor vehicles.
• Verify the code using an OBD-II scanner.
• Check the VIN stored in the transfer case module and PCM.
• Inspect wiring and connections between the modules.
• Reprogram the transfer case module with the correct VIN.
• Replace the transfer case module with a compatible unit.
• Repair or replace faulty wiring and connections.
• OBD-II scanner
• Multimeter
• Reprogramming tool
$150 - $500
Moderate
• Chevrolet Silverado
• GMC Sierra
• Ford F-150
• Ensure proper programming when replacing components.
• Regular maintenance checks on transfer case system.
• Use OEM parts for replacements.
Compatibility Issue
• Consult a professional mechanic for accurate diagnosis.
• Avoid using non-compatible parts from other vehicles.
• Keep records of any replacements or repairs.
Check with your vehicle manufacturer for warranty coverage on drivetrain components.
This code has become more common with the increased use of electronic control modules in modern vehicles.
Moderate – It's important to address this issue to ensure proper 4WD functionality.
Driving with a malfunctioning transfer case can lead to loss of vehicle control, especially in off-road or slippery conditions.
• Vehicle must be in park or neutral.
• Ensure all electrical connections are secure.
The transfer case is located between the transmission and the drive shaft, typically underneath the vehicle.
Q: Can I drive with this code?
A: It's not recommended to drive with this code as it may affect the vehicle's ability to switch between 2WD and 4WD.
Q: How do I know if the transfer case module is faulty?
A: A diagnostic scan and inspection by a professional can determine if the module is faulty.
Pro · Four-system diagnostics
A handheld scanner aimed at engine, transmission, ABS, and airbag diagnostic work.
Chassis and ABS faults usually need a scanner that can read brake-system data directly.
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Universal · Torque wrench
Useful when reassembly torque matters for wheel, suspension, and under-hood fasteners.
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Helpful for safer access during underbody inspection work.
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