ABS Warning Light On in a BMW M5 F90? Here’s What to Check First

If the ABS warning light is staying on continuously in your BMW M5 F90, it’s natural to feel a bit uneasy. In my experience, the most common cause on these cars is a faulty wheel speed sensor or something related to its circuit — like a damaged tone ring, a corroded connector, or chafed wiring. But it’s not the only possibility, and a proper diagnosis will save you from buying parts you don’t need.

Likely Causes

• Wheel speed sensor – These sensors live at each wheel and can become dirty, damaged, or simply fail over time. On most F90 models, each sensor is a separate part that can be replaced individually; you don’t usually need to change the whole hub or bearing assembly just for a sensor.
• Tone ring / reluctor ring – The sensor reads a toothed ring, and if a tooth is broken or the ring is cracked, the signal drops out. In many modern BMWs this ring is part of the wheel bearing/hub assembly, so replacement might involve the bearing — but that’s a different job than swapping the sensor.
• Wiring or connector – A loose, corroded, or water-damaged connector at the wheel can trigger the light even if the sensor itself is fine. Checking these first is always worth the ten minutes.
• ABS control module – Less commonly, the module itself develops an internal fault or a poor connection on its main harness plug. This is a diagnosis of exclusion after the other items look good.

Where to Start Checking

Before tearing anything apart, read the fault codes with a BMW-compatible scan tool. The code will usually tell you which wheel is misbehaving, and sometimes whether it’s a signal or supply/ground issue. Then visually inspect that sensor’s connector and wiring for obvious damage, and check the sensor tip for metallic debris or wear. You can also measure the sensor’s resistance and compare it to a known-good wheel if you have wiring diagrams handy. If everything looks clean but the light persists, testing the sensor output while spinning the wheel — using an oscilloscope or a diagnostic tool that can graph live sensor data — will often reveal a broken tone ring.

Is It Safe to Drive?

With the ABS light on, your normal hydraulic brakes will still work — the car will stop, but without the anti-lock function. That means on slippery or wet roads, the wheels can lock up under hard braking, and you may also notice features like stability control and traction control are disabled or restricted. So while you can usually drive to a garage or home, it’s safest to avoid aggressive braking and high speeds in rain or snow, and to have the system diagnosed and repaired as soon as practical. Be aware that some regions require a functioning ABS for roadworthiness, so check your local rules as well. And before buying any parts, confirm the exact sensor and connector type for your car’s model year and region — the F90 M5 uses different components across production dates, and a quick part number check will prevent ordering the wrong piece.

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