Subaru Tech Tip: Error Codes Following Wheel Bearing Hub Replacement

Subaru Tech Tip: Error Codes Following Wheel Bearing Hub Replacement

On the affected vehicles, improper installation of a new hub assembly may cause an ABS, cruise control and/or VDC fault code to occur.

On the hubs for 2005-2014 Subaru Legacy and Outback applications, a speed sensor mounts into the knuckle. It’s exposed end extends out behind the bearing to capture pulses from an encoder ring on the back of the bearing. (The encoder ring is permanently adhered to the wheel bearing outer shell and is not serviceable.)

On the affected vehicles, improper installation of a new hub assembly may cause an ABS, cruise control and/or VDC fault code to occur.

Overview

On the hubs for these applications, a speed sensor mounts into the knuckle. Its exposed end extends out behind the bearing to capture pulses from an encoder ring on the back of the bearing. (The encoder ring is permanently adhered to the wheel bearing outer shell and is not serviceable.)

Photo 1


As the wheel rotates, the encoder ring’s small magnetic strips (see Photo 1) create pulses that the speed sensor’s Hall element (see Photo 2) picks up and outputs at a frequency proportional to the wheel speed. Each wheel’s speed signal is transmitted to the ABS and/or VDC module (depending on how the vehicle is equipped), then to the ECM. Cruise control is managed by the ECM. (See Photos 1 and 2.)

Photo 2

 

On most vehicles, a problem with this speed signal would trigger an ABS code first. It is possible, however, for a speed signal problem to trigger a cruise control fault. Once a cruise control fault is set, it will not re-engage until the ignition switch is cycled (clearing the code).

Any ABS, VDC or cruise control fault code should undergo proper diagnosis to determine the source of the problem, which could be: the speed sensor, sensor air gap, connections, signal interference (radio wave or foreign particles) or the bearing’s magnetic encoder ring.

Inspection Procedure

Figure 1

Hub and Speed Sensor Inspection Check for Rust: Any rust present on the mounting area or on the backing plate can keep the bearing assembly from being fully seated (even when it’s torqued down), creating an excessive “air gap” between the encoder and the sensor. It takes only a few extra thousandths of an inch to trigger the false error codes. (See Fig. 1.)

Photo 3

In addition, during reassembly, any rust that’s present on the knuckle or backing plate may be dislodged and will adhere to the magnetic encoder ring of the new hub assembly. Also, check for any dirt, grease or metal particles on the tip of the sensor. Any of these conditions will cause interference within the magnetic field and will result in the pulse being erratic or blocked altogether. (See Photos 3, 4 and 5.)

Photo 4

 

Photo 5

Installation Procedure

Photo 6

It is imperative that all the components that are involved in reassembly be thoroughly cleaned of rust, scale, grease, dirt and any other contaminants. Using a wire brush attachment, clean the knuckle face. Using an abrasive brush with a rotary tool, clean the inside of the knuckle and backing plate of any loose rust and scale. Follow up with compressed air and brake cleaner spray to clean the knuckle and backing plate surfaces. Once all of the components have been cleaned, follow the factory service manual for hub assembly installation and proper torquing procedure. This vehicle requires the hub assembly to be torqued to 140 ft./lbs. with no load on the hub. (See Photo 6.)

Courtesy of MOOG Problem Solver.

You May Also Like

How Capacitors Protect Ignition Circuits

A capacitor is a two-terminal electrical device that stores and releases energy as an electric charge.

If you look at some ignition system wiring diagrams, you may notice something unexpected on the ground connection for the coils on some BMW models: it is a capacitor. 

I was stumped! So, I emailed Philip Austin, NGK’s Manager of Technical Training. He quickly shot back: “Since it’s on the power feed side, it plays the role of keeping the energy constant as the coil is fired and/or ready to fire during each cycle of firing.”

Driveshaft Diagnostics

The big challenge with late-model vehicles is the diversity of driveshafts. 

Mercedes-Benz Engine Oil Leaks

Mercedes makes a fine product, but certain repairs will emerge as trends over time.

Steering Angle Sensor 101

The steering angle is used by many ADAS functions.

Electric Power Steering

Today’s systems have been refined.

Other Posts

Freeze Frame Diagnostics

Freeze frame data is a “snap shot” of when the code occurs of the specific sensor PIDs.

Understanding BMW 12V Lithium Ion Battery Technology

Let’s dig into this type of battery construction and all it has to offer.

Audi Quattro

The system’s goal has remained the same over the years: maximizing traction by sending power to all four wheels.

Threadlocking Compounds For Vehicle Corners

To get the most out of these “liquid” tools, you first need to know how they work.