DTC C1155 OBDII is a factory-specific code whose setting occurs at the moment that the PCM (Powertrain Control Module) founds an error in the circuit that relates to the Left Front Wheel Speed Sensor. This type of sensor is a Hall effect sensor, which creates magnetic fields once the teeth of a reluctor ring pass in front of the sensor as the ring rotates with the wheel. Although this ring is usually attached to the drive shaft, it is also incorporated into the wheel bearing.
The teeth of the reluctor rings are closely related to the wheel speed sensors and are located evenly around the circumference of the ring. The signals generated as the ring rotates are evenly spaced, making it possible for the PCM to count the number of signals produced for each complete revolution of a wheel and the number used as a basis for the PCM to calculate the rotational speed of each wheel.
All Wheel Speed Sensors are first connected to the ABS Brake Control Module and from there the connection goes out to the PCM. This is important because the ABS module uses the rotational speeds of each individual wheel to determine the proper braking forces, thus preventing the lock-up of one or more wheels in difficult driving conditions. Safety-critical systems depend entirely on accurate signals from the wheel speed sensors. In the event of a sensor or sensor circuit failure, the PCM or ABS will recognize that effective control of these safety systems has not been achieved.