Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
The car's computer isn't getting any information from the sensor that tells it how fast the right back wheel is turning.
The wheel speed sensor is responsible for sending information about the speed of each wheel to the car's computer. This code indicates that there is no signal coming from the right rear wheel speed sensor.
The C121F code is triggered when the ABS (Anti-lock Braking System) module does not receive a signal from the right rear wheel speed sensor. This sensor is crucial for monitoring wheel speed and ensuring proper ABS function.
• ABS warning light on
• Traction control light on
• Inoperative ABS or traction control
• Faulty right rear wheel speed sensor
• Damaged or corroded wiring or connectors
• Faulty ABS module
ABS: Anti-lock Braking System
OBD-II: On-Board Diagnostics, second generation
• Inspect the right rear wheel speed sensor for damage.
• Check the wiring and connectors for corrosion or damage.
• Test the sensor signal with a multimeter.
• Replace the right rear wheel speed sensor.
• Repair or replace damaged wiring or connectors.
• Replace the ABS module if necessary.
• Multimeter
• OBD-II scanner
• Socket set
$100 - $300
Moderate
• Dodge Charger
• Chrysler 300
• Jeep Grand Cherokee
• Regularly inspect wheel speed sensors and wiring.
• Keep ABS components clean and dry.
• Avoid driving through deep water.
Sensor Issue
• Have the vehicle inspected by a professional if the ABS light is on.
• Do not ignore the warning lights as they affect braking performance.
Wheel speed sensors may be covered under the vehicle's powertrain or bumper-to-bumper warranty. Check with the manufacturer.
This code has been commonly associated with vehicles that have high mileage or have been exposed to harsh environmental conditions.
Moderate – While the vehicle can still be driven, the ABS and traction control systems may not function properly, affecting safety.
Driving with a malfunctioning ABS system can increase the risk of accidents, especially in slippery conditions.
• Vehicle must be in motion for the sensor to generate a signal.
• Ensure the vehicle is on a flat surface for accurate testing.
The right rear wheel speed sensor is located near the wheel hub on the right rear wheel.
Q: Can I drive with a C121F code?
A: Yes, but it's not recommended as the ABS and traction control may not work, affecting safety.
Q: How can I reset the ABS light?
A: Fix the underlying issue first, then use an OBD-II scanner to clear the code.
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.
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