ABS fault diagnosis and repair

What is ABS, and why do fault codes appear?

ABS (Anti-lock Braking System) prevents wheels locking up under hard braking so you keep steering control. The system consists of wheel speed sensors (one per wheel), a hydraulic control unit (HCU) with pump and valves, and an electronic control unit (ECU). ABS is also tied to ESC (Electronic Stability Control) and traction control. When one component delivers incorrect signal, a fault code is stored and the dashboard ABS light comes on. Often ESC is disabled at the same time — the car still drives, but without the assistance systems.

Common fault codes and causes

By far the most common ABS fault is a defective wheel speed sensor. The sensor sits at each wheel bearing and reads a toothed ring. After a few years of road salt, water spray and dirt the wires can corrode, contacts oxidise or the sensor head itself become damaged. Other common causes are rust on the toothed ring (especially older cars), faulty hydraulic unit, low battery voltage disturbing the modules, or loose plugs after earlier repair.

Symptoms and warning signs

ABS dashboard light is the obvious sign, often together with ESC, traction control and hill-hold lights. The car may also show messages like "ABS fault — contact workshop". Pedal feel may be normal until hard braking — at that point you notice the car doesn't activate ABS as usual (no pulsing in the pedal). The car still drives with normal brakes, but the shorter braking distance ABS gives you on wet or slippery surfaces is gone, sharply increasing risk.

What we do at the workshop

We start with an OBD fault read to retrieve all stored codes from the ABS module and related modules (ESC, engine). Codes often show which wheel has the fault. Then a physical inspection: we check sensor cables for damage, contact pins for corrosion, and the toothed ring for rust or damage. Live data via OBD shows whether the sensor produces signal during wheel rotation — zero or erratic signal is what we look for.

Once the fault source is confirmed we replace the defective component — typically a wheel speed sensor (1,500–3,500 NOK per piece including labour). After repair we clear the codes and run a test drive to verify the ABS light is off and the system functions dynamically.

Original or aftermarket parts?

OE wheel speed sensors last longest, but quality brands like Bosch, FAE and VDO deliver good quality at lower price. We never recommend the cheapest no-name sensors — they often throw fault codes again within months.

What about the warranty?

Repair at an authorised workshop does not affect the new-car warranty. We give 12 months' guarantee on work and parts.

Book online easily or call us on 41 17 32 24.

Frequently asked questions

Can I drive with an ABS fault?

The car is drivable with normal brakes, but ABS is disabled. That means wheels can lock on wet or slippery surfaces under hard braking, and braking distance gets significantly longer. ESC and traction control are usually also disabled. We recommend repair as soon as possible — especially before winter.

How much does a wheel speed sensor cost?

A new wheel speed sensor plus labour is typically 1,500–3,500 NOK depending on car model and accessibility. We always provide a fixed quote after diagnosis.

Does an ABS fault affect the periodic inspection?

Yes. ABS dashboard light is a check point at periodic inspection and results in a defect note. You must repair before next inspection.

Can I clear the ABS fault code myself?

You can clear the code with an OBD scanner, but if the fault itself isn't repaired the code returns within a short time. It's almost always faster and cheaper to diagnose properly once.

Brake service