ABS rings on HGVs: what they do and what happens when they fail
The ABS ring is a toothed metal ring mounted on the hub or axle shaft. As the wheel turns, the teeth pass a magnetic sensor and generate an AC signal. The EBS or ABS control unit reads this signal to calculate wheel speed on each axle independently. If the ring is damaged, corroded, or has missing teeth, the signal becomes erratic or drops out entirely, and the system triggers a fault code.
On most modern HGVs, a single ABS fault code is not an immediate roadworthiness failure but it will be flagged at annual test. Two or more ABS faults that disable the system are a test failure. Check ring-to-sensor air gap at the time of replacement.
Frequently Asked Questions
Can I drive an HGV with a faulty ABS ring?
A faulty ABS ring will trigger a warning light and may disable the ABS or EBS system depending on how many sensors are affected. The vehicle remains legal to drive with a single ABS sensor fault in most cases, but EBS faults that disable the braking system are a roadworthiness concern. Address ABS ring faults promptly.
How do I know if the ABS ring is the fault rather than the sensor?
Use a diagnostic scan tool to read the fault code and check the live sensor data. A sensor that reads zero or shows an erratic signal on one corner is consistent with either a ring fault or a sensor fault. Visually inspect the ring for damage, missing teeth, or heavy corrosion before replacing either component.
Are ABS rings pressed on or bolted?
Both designs are used on HGVs. Most steer axle ABS rings are press-fit onto the hub. Some drive axle rings are integral to the hub assembly or flange. Confirm the fitment design for your specific axle before ordering.
Does the ABS ring need to be timed to the hub when fitted?
Press-fit rings do not require timing and can be fitted in any rotational position. Ensure the ring seats fully and squarely against the hub face. Check the air gap to the sensor after fitting.
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