ABS Light Stays On in Your Mercedes-Benz CLA? Likely a Wheel Speed Sensor

If your Mercedes-Benz CLA (C118) has its ABS warning light on continuously, the most common culprit is a wheel speed sensor. On the C118, each wheel is fitted with a sensor that reports rotational speed to the ABS/ESP control unit. When one sensor signal is missing or implausible, the system switches off ABS and stability assist and lights the warning lamp. The sensor isn't the only possible cause — wiring, connectors, or the tone ring can also be at fault — but that's where a good diagnosis starts.

What to check first

Before buying anything, get the fault codes read with a proper diagnostics tool. That will usually tell you which wheel sensor is involved. Then inspect:

• Wiring and connectors at the wheel: Look for chafed wires, corrosion, or a loose plug.
• The sensor itself: It can be fouled by metal shavings or debris; sometimes cleaning it is enough.
• The tone ring / reluctor ring: A cracked or damaged ring can cause erratic signals.
• Wheel bearing play: Excessive play can disturb the sensor gap and produce intermittent faults.

On most C118 models the wheel speed sensor is a separate part from the wheel hub or bearing, so replacing just the sensor is usually sufficient. Full hub or bearing assembly replacement is a fallback when the tone ring or bearing itself is damaged — and that's not the first thing to assume.

Is it safe to keep driving?

Your CLA will still drive and the normal braking system will work, but ABS, ESP, and hill-start assist may be inactive. That means on wet, snowy, or loose surfaces your wheels can lock up and the car can skid under hard braking. It's usually fine to drive gently to a repair shop, but I wouldn't put off the repair or take it on long motorway trips in bad weather. If the brake warning light is also on, that points to a different, more urgent problem — low brake fluid or hydraulic trouble — so have it checked immediately.

A proper scan will pinpoint the faulty wheel in a few minutes, and the repair is often straightforward. Just confirm the exact sensor and fitting procedure for your specific model year and region, because part numbers and connectors can vary. That way you avoid buying the wrong component — and you'll know exactly what you're dealing with.

This material is AI-generated and for informational purposes only — it does not replace an in-person diagnosis by a qualified mechanic.