Speed Wheel Sensor RF Input Circuit Failure

OBD II fault code C1145 is a manufacturer-specific trouble code that is defined by carmaker Ford as “Speed Wheel Sensor RF Input Circuit Failure” and is set when the PCM (Powertrain Control Module) detects a failure, defect or malfunction in the input circuit of wheel speed sensor on the right front wheel. All modern vehicles use dedicated sensors located at each wheel to monitor wheel speed.

The purpose of measuring wheel speed is to supply the ABS and other control modules with information on the rotational speed of each wheel. The principal user of this information is the ABS control module, which has the function of modulating brake pressure to wheels that rotate at slower rates than others do during braking to maximize braking performance by preventing wheels from locking up during aggressive braking.

As a practical matter, a wheel speed sensor generates magnetic signals when the teeth on a rotating reluctor ring pass in front of the sensing element, which signals are converted into voltages by the ABS control module. Thus, by “counting” the number of signals at each wheel, the ABS, or other control modules can compare the frequency of the signals at each wheel as a means of calculating the rotational speed of each wheel relative to all the other wheels.

While this data is primarily used by the ABS system to modulate brake pressure at individual wheels during aggressive braking events, the same data is also used by other control modules. For instance, the traction control system applies modulated brake pressure to a spinning wheel to transfer torque to the non-spinning wheel, while the stability control system can supply modulated braking forces to individual wheels to force the vehicle into following a line dictated by the steering angle sensor.

Similarly, hill descent control system use this data to apply braking forces to all the wheels to control the vehicle’s speed when negotiating steep descents, while accident mitigation systems use this data to apply more braking force (sometimes autonomously) to the wheels than a driver could, while preventing wheels from locking up at the same time. From the above, it should be obvious that wheel speed sensors are safety-critical components in any modern vehicle’s brake system.

Therefore, if the PCM or any other control module detects a fault, failure, or defect in the right front wheel speed sensors’ circuit(s) that interrupts the communication between the right front wheel speed sensor and implicated control modules, one or more control modules will set code C1145 and illuminate all relevant waning lights as result.