Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
The car can't tell how fast the left front wheel is spinning because it can't get a signal from the sensor.
The left front wheel speed sensor is not sending any signal to the car's computer, which is necessary for systems like ABS to function properly.
The C121C code indicates that the vehicle's ABS module has detected a loss of signal from the left front wheel speed sensor. This sensor is crucial for monitoring the rotational speed of the wheel and is used by the ABS system to prevent wheel lock-up during braking.
• ABS warning light illuminated
• Traction control system may be disabled
• Increased stopping distance
• Faulty left front 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 left front wheel speed sensor and its wiring for damage.
• Check the connector for corrosion or poor connection.
• Use a multimeter to test the sensor's resistance and signal output.
• Replace the faulty wheel speed sensor.
• Repair or replace damaged wiring or connectors.
• Replace the ABS module if necessary.
• Multimeter
• OBD-II scanner
• Socket set
$150 - $400
Moderate
• Dodge Charger
• Jeep Grand Cherokee
• Chrysler 300
• Regularly inspect wheel speed sensors and wiring.
• Avoid driving through deep water to prevent sensor damage.
• Keep the wheel area clean to prevent debris buildup.
Sensor Issue
• Avoid hard braking until the issue is resolved.
• Drive cautiously, especially in wet or icy conditions.
Check with the vehicle manufacturer for warranty coverage on ABS components.
This code has been commonly reported in vehicles with high mileage or those frequently driven in harsh conditions.
Moderate – While the vehicle is still drivable, the ABS system may not function correctly, affecting braking performance.
Driving with a malfunctioning ABS system can increase stopping distance and reduce vehicle control in emergency braking situations.
• Vehicle must be driven at a speed where ABS would typically engage.
• Dry and safe road conditions for testing.
The left front wheel speed sensor is located near the wheel hub assembly on the left front wheel.
Q: Can I drive with a C121C code?
A: While you can drive, it's not recommended as your ABS may not function properly, affecting braking performance.
Q: How do I reset the ABS light after fixing the issue?
A: After repairing the issue, use an OBD-II scanner to clear the code, or the light may reset itself after a few driving cycles.
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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