C1239 Volvo Foreign Object Attached On Tip Of Left Rear Sensor

Possible causes

– Faulty Left Rear Speed Sensor
– Left Rear Speed Sensor rotor
– Sensor installation
– Brake actuator (skid control ECU)

Symptoms

– ABS warning light ON

C1239 Volvo OBD Code Description

The speed sensor detects wheel speed and sends the appropriate signals to the ECU. These signals are used to control the ABS control system. The front and rear rotors have 48 serrations each.

When the rotors rotate, the magnetic field emitted by the permanent magnet in the speed sensor generates AC voltage. Since the frequency of this AC voltage changes in direct proportion to the speed of the rotor, the frequency is used by the ECU to detect the speed of each wheel.