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 front wheel is spinning.
The wheel speed sensor measures the speed of the wheel and sends this information to the vehicle's control systems. If there's no signal, the system can't determine the wheel's speed.
The C121D code indicates that the ABS (Anti-lock Braking System) module is not receiving a signal from the right front wheel speed sensor. This sensor is crucial for monitoring the speed of the wheel and ensuring proper ABS function.
• ABS warning light illuminated
• Traction control light on
• Inoperative ABS system
• Faulty right front wheel speed sensor
• Damaged sensor wiring or connector
• Malfunctioning ABS module
ABS: Anti-lock Braking System
OBD-II: On-Board Diagnostics, Second Generation
• Inspect the right front wheel speed sensor and its wiring.
• Check for any corrosion or damage on the sensor connector.
• Test the sensor with a multimeter for proper resistance.
• Replace the faulty right front wheel speed sensor.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ABS module if necessary.
• Multimeter
• OBD-II scanner
• Socket set
$100 - $300
Moderate
• Dodge Charger
• Jeep Grand Cherokee
• Chrysler 300
• Regularly inspect wheel speed sensors for damage.
• Keep sensor areas clean and free of debris.
• Ensure proper wheel alignment and balance.
Sensor Issue
• Avoid driving at high speeds until the issue is resolved.
• Have the vehicle inspected by a professional mechanic.
Check with the vehicle manufacturer for specific warranty coverage related to the ABS system.
This code has been commonly reported in vehicles with high mileage or those driven in harsh conditions.
Moderate – The vehicle can still be driven, but ABS functionality may be compromised.
Driving with a malfunctioning ABS system can increase stopping distances and reduce control during emergency braking.
• Vehicle parked on a level surface
• Ignition in the 'on' position
The right front wheel speed sensor is located near the brake rotor on the right front wheel.
Q: Can I drive with a C121D code?
A: Yes, but it's not recommended as the ABS may not function properly, affecting braking performance.
Q: How do I know if the wheel speed sensor is bad?
A: Symptoms include an ABS warning light and possible erratic braking behavior.
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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