C-Class W206 ABS Light Staying On? Wheel Speed Sensor Diagnosis

If your Mercedes-Benz C-Class W206 has its ABS warning light glowing solidly rather than fading out after start-up, the system has found a fault and disabled itself. On this generation, the most common source is one of the four wheel speed sensors. Each sensor counts how fast its wheel turns, and when the signal is missing or implausible, the ABS, stability control and sometimes brake-assist switch off.

Likely causes and what to check

• Wheel speed sensor failure: On many W206 models the sensor is available separately, so replacing just the affected sensor usually restores full function. A wheel bearing/hub assembly replacement is a fallback when the encoder ring is damaged or when your specific vehicle’s parts diagram shows them as one unit.
• Wiring or connector damage: Inspect the sensor line where it runs to the wheel well — a frayed wire, corroded connector or broken retainer produces the same solid ABS light.
• Tone ring or encoder ring issues: A cracked ring or a damaged tooth can confuse the sensor and keep the warning lit.
• Low brake fluid: Unlikely, but easy to check at the reservoir before replacing parts.

Is it safe to drive?

In normal, dry conditions the brakes still work, so you won’t be left without stopping power. But ABS and stability control are typically disabled, which means wheels can lock in an emergency stop and the car may feel unstable on wet or loose surfaces. If the red brake warning comes on as well, or the pedal feels soft, drive no further and have the car recovered.

Because the warning stays on continuously, the fault is likely constant rather than intermittent, which makes diagnosis easier. A diagnostic scan will point your mechanic to the specific wheel, and a quick look at the sensor and its wiring tells them whether a new sensor or a cable repair is needed. Have it looked at soon — every Mercedes owner wants those safety systems ready when they’re truly needed.

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