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 is having trouble getting a signal from the sensor that checks how fast the left rear wheel is spinning.
The code C0661 indicates that the voltage signal from the left rear wheel speed sensor is below the expected range.
The left rear wheel speed sensor is responsible for sending the speed data of the wheel to the vehicle's Electronic Control Unit (ECU). A 'Circuit Low' error suggests that the voltage or signal from this sensor is lower than the ECU expects, which could be due to wiring issues, a faulty sensor, or a problem with the ECU itself.
• ABS warning light on
• Traction control system malfunction
• Inaccurate speedometer readings
• Faulty wheel speed sensor
• Damaged or corroded wiring or connectors
• Faulty ECU
ECU: Electronic Control Unit
ABS: Anti-lock Braking System
• Check for any visible damage to the wheel speed sensor and wiring.
• Use a multimeter to test the voltage and resistance of the sensor.
• Inspect the ECU for any fault codes or malfunctions.
• Replace the faulty wheel speed sensor.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ECU if necessary.
• Multimeter
• OBD-II scanner
• Basic hand tools
$100 - $300
Moderate
• Chevrolet Silverado
• GMC Sierra
• Cadillac Escalade
• Regularly inspect wheel speed sensors and wiring.
• Keep the vehicle's undercarriage clean to prevent corrosion.
• Address ABS warning lights promptly.
Sensor Issue
• Do not ignore the ABS warning light.
• Consult a professional mechanic if unsure about the repair.
Check with your vehicle manufacturer for specific warranty coverage on ABS components.
This code has been commonly associated with vehicles experiencing ABS issues due to sensor or wiring faults.
Moderate – While the vehicle is still drivable, ABS and traction control systems may not function properly.
Driving with a malfunctioning ABS system can increase stopping distances and reduce vehicle control during emergency braking.
• Vehicle stationary
• Ignition on
The left rear wheel speed sensor is located near the wheel hub assembly of the left rear wheel.
Q: Can I drive with code C0661?
A: Yes, but be cautious as your ABS and traction control may not work properly.
Q: How do 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.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.