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What does code C0055 mean?

Code C0055 stands for Rear Wheel Speed Sensor Circuit.

The anti-lock brake system (ABS) prevents wheel lockup during emergency braking. This is accomplished by modulating brake pressure to the appropriate wheels. In essence, the ABS system "pumps" the brakes in a panic stop.

An ABS system is composed of several components. The heart of the system is the ABS module - a computer designed to control the ABS system. Sometimes the ABS module may be called other names, such as the electronic brake control module (EBCR). Wheel speed sensors are the main input to the ABS module. The module uses this information to determine when to apply and release the brakes.

Anti-lock Brake System

Most wheel speed sensors (WSS) produce a voltage in relation to the changing magnetic field that occurs as the wheel rotates. A toothed ring (called a reluctor) is mounted on the axle shaft or wheel hub, which rotates with the wheel assembly. As the rings turns past the WSS, it causes the sensor to produce an alternating current (AC) voltage. The frequency and amplitude of the sensor signal increases as the wheel turns faster.

While most modern vehicles use four wheel speed sensors, some use less. Pickup trucks in particular often only use one rear wheel speed sensor, or vehicle speed sensor (VSS). When a VSS sensor is used, the sensor signal is typically sent to the engine control module (ECM). The ECM then shares the VSS information with the ABS module.

Code C0055 indicates the ABS module has determined a problem with the rear wheel speed sensor (vehicle speed sensor) or its circuit.

Get it diagnosed by a professional

C0055 symptoms

Common causes for C0055

Code C0055 is typically caused by one of the following:

  • A faulty wheel speed sensor/vehicle speed sensor
  • Wiring problems
  • Control module problems

How to diagnose and repair C0055

Perform a preliminary inspection

Sometimes C0055 can pop up intermittently. Clear the code and see if it returns. If it does, the next step is to perform a visual inspection. A trained eye can check for issues such as broken wires and loose connections. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time.

Check for other DTCs

Additional diagnostic trouble codes (DTCs) may indicate problems elsewhere that are affecting wheel speed sensor operation. Any additional DTCs should be addressed prior to diagnosing C0055.

Scan tool check

Typically, a technician will begin by checking VSS operation with a diagnostic scan tool. This tool connects directly to the vehicle's diagnostic port, where it can gain access to vehicle data. Then the vehicle can be driven while monitoring wheel speed sensor values. The value for the VSS should increase with vehicle speed. If the value does not increase, there is a problem with the VSS or its circuit.

Check the VSS

The next step is to determine if the problem is with the VSS itself or the circuit. A technician will test the VSS directly using a digital multimeter (DMM) or digital storage oscilloscope (DSO). Either can be connected directly to the VSS while the turning wheels (or speedometer). As the wheels are turned, the VSS should produce an AC voltage reading. If it does not, the sensor is faulty and should be replaced.

Check the WSS circuit

At this point, the VSS sensor performed OK when tested directly, but did not register properly on the scan tool. This indicates the VSS signal is not registering at the ABS module, potentially due to a problem with the circuit. The circuit can be tested for excessive resistance, shorts and opens using a DMM. If a problem is found, the factory wiring diagram will need to be traced to pinpoint the concern. Then any necessary repairs can be made.

Check the ABS module

In very rare instances, the ABS module or ECM, may not be reading the VSS properly. In this case, the module would need to be either reprogrammed or replaced.

Other diagnostic codes related to C0055

No codes are directly related to C0055.

Code C0055 technical details

C0055 is often set with sub-codes which can help with diagnosis. This is an example from a GM vehicle.

  • C0055 00: Code C0055 00 indicates the ABS module has detected a short to ground, short to voltage, open/high resistance, on the rear wheel speed sensor signal circuit.
  • C0055 5A: Code C0055 5A indicates the ABS module has detected an erratic rear wheel speed signal.
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