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 a signal from the sensor that tells how fast the back left wheel is spinning.
The left rear wheel speed sensor is responsible for sending data about the wheel's speed to the car's computer. If it doesn't send a signal, the computer can't monitor that wheel's speed.
The C121E code indicates that the vehicle's ABS (Anti-lock Braking System) module has detected no signal from the left rear wheel speed sensor. This sensor is crucial for monitoring the wheel's speed and ensuring proper ABS function.
• ABS warning light on
• Traction control light on
• Inoperative ABS system
• Faulty wheel speed sensor
• Damaged wiring or connectors
• Malfunctioning ABS module
ABS: Anti-lock Braking System
OBD-II: On-Board Diagnostics II
• Inspect the left rear wheel speed sensor for damage.
• Check the wiring and connectors for continuity and damage.
• Test the ABS module for proper function.
• Replace the faulty wheel speed sensor.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ABS module if necessary.
• OBD-II scanner
• Multimeter
• Wheel speed sensor removal tool
$100 - $300
Moderate
• Dodge Charger
• Jeep Grand Cherokee
• Chrysler 300
• Regularly inspect wheel sensors and wiring.
• Avoid driving through deep water or mud.
• Perform routine ABS system checks.
Sensor Issue
• Drive cautiously if the ABS light is on.
• Get the vehicle inspected by a professional mechanic.
Check if the vehicle's warranty covers ABS components.
This code has been associated with sensor failures in vehicles with high mileage or after exposure to harsh conditions.
Moderate – ABS may not function properly, affecting braking performance.
Driving with a malfunctioning ABS system can increase stopping distances and reduce control during braking.
• Vehicle stationary
• Engine running
The left rear wheel speed sensor is located near the brake rotor on the rear left wheel.
Q: Can I drive with the C121E code?
A: While you can drive, it's not recommended as the ABS system may not function properly.
Q: How do I reset the ABS light?
A: Fix the underlying issue and 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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