Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This means that the part of the car that helps it switch between 2-wheel and 4-wheel drive is asking for power when it shouldn't because the brakes are on.
The transfer case control module is requesting torque even though the brake signal is active, which is not expected behavior.
The P166B code indicates that the Transfer Case Control Module (TCCM) is requesting torque from the engine when the brake pedal is pressed. This is an unexpected condition and can indicate a fault in the TCCM or related components.
• Check Engine Light is on
• Unusual behavior in 4WD system
• Possible braking issues
• Faulty Transfer Case Control Module
• Wiring issues in the TCCM circuit
• Faulty brake pedal position sensor
Transfer Case: A part of the drivetrain that transfers power from the transmission to the front and rear axles.
Torque: A measure of rotational force applied by the engine.
• Use an OBD-II scanner to confirm the P166B code.
• Inspect the wiring and connections to the Transfer Case Control Module.
• Check the brake pedal position sensor for proper operation.
• Repair or replace faulty wiring or connections.
• Replace the Transfer Case Control Module if faulty.
• Replace the brake pedal position sensor if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$200 - $600
Moderate
• Ford F-150
• Chevrolet Silverado
• Jeep Grand Cherokee
• Regular maintenance of the transfer case system
• Periodic inspection of wiring and connectors
• Ensure brake system is functioning properly
Control Module Issue
• Avoid using 4WD until the issue is resolved.
• Consult a professional mechanic for accurate diagnosis.
Check with the vehicle manufacturer for warranty coverage on drivetrain components.
This code has been associated with issues in vehicles equipped with electronic transfer case systems.
Moderate – It should be addressed soon to avoid potential drivetrain or braking issues.
Driving with this fault may affect vehicle handling and safety. Address promptly.
• Vehicle stationary with engine running
• Brake pedal pressed
The Transfer Case Control Module is typically located near the transfer case or under the dashboard.
Q: Can I drive my car with the P166B code?
A: It's not recommended as it may affect the vehicle's handling and safety.
Q: Will this code cause my vehicle to stop working?
A: Not immediately, but it can lead to further issues if not addressed.
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.
Useful when wheel, hub, or suspension hardware needs correct reassembly torque.
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Universal · Drive-on ramps
Helpful for safer access underneath the vehicle during exhaust, EVAP, and underbody inspection work.
Helpful for safer access during underbody inspection work.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.