ABS warning light on the dashboard

Warning: ABS is a safety device (expert-only safety lock). The ABS wheel sensor reads the passing teeth of a toothed ring fixed to the wheel, from a very short distance (the air gap, often around 0.5 to 1 mm). Its tip is often magnetized, which attracts metal filings; combined with mud, brake dust, and road debris, it gets fouled and the signal degrades. An impact or a disassembly can also shift the sensor out of position (incorrect air gap). The control unit, receiving an inconsistent or absent signal, disables ABS as a precaution and lights the warning. This is the most frequent cause, and often the simplest: cleaning the sensor and the toothed ring, and checking the air gap, is enough in many cases. The tell: the light goes out at ignition (system self-test OK) then comes back on while riding (as the fouled sensor throws off the reading), and visual inspection reveals a dirty or misaligned sensor. Although cleaning is accessible, this involves a safety component, and reliable diagnosis (distinguishing fouling, misalignment, a dead sensor, or a damaged toothed ring) requires reading/clearing the fault code with a diagnostic tool: this cause is therefore rated expert-only and referred to a professional. In the meantime, the regular brakes still work — avoid emergency stops.

Warning: a safety component (expert-only safety lock). Beyond simple fouling, the ABS wheel sensor can be genuinely out of service: a cut or damaged power/signal wire (the sensor sits exposed near the wheel, subject to debris and suspension movement), a corroded connector, or a broken internal coil. In this case, no valid signal reaches the control unit, which disables ABS and keeps the warning on permanently. The symptom resembles a fouled sensor (light coming back on while riding), but cleaning won't fix it: the sensor needs replacing. Precise diagnosis relies on a diagnostic tool (the fault code identifies the wheel and the nature of the fault) and on checking the sensor and its wiring (continuity, resistance). Since this involves a safety device and replacement must be followed by clearing the code and a test ride, this cause is rated expert-only and left to a professional. The distinguishing tell versus fouling: a visibly torn/cut wire, a cracked sensor, or a warning that persists after cleaning. As always, the regular brakes remain functional without ABS: ride carefully and avoid hard braking until it's repaired. A new ABS sensor costs roughly a few dozen to over a hundred euros depending on the model.

Repair to be left to a professional.

The ABS system has its own power circuit, protected by a dedicated fuse, along with its own wiring harness and connectors. A blown ABS fuse, a loose terminal, or a corroded connector cuts power to the whole system: the control unit stops working and the ABS warning comes on, generally right from ignition and staying on. This is a relatively accessible cause to check, and the only ABS warning cause that doesn't necessarily need a diagnostic tool for a first check: locate the ABS fuse (fuse box cover), verify it's intact, and inspect the ABS circuit's connectors. The tell: a warning light on right from ignition that never goes out (power cut), rather than a light that comes back on while riding (sensor). Replacing a fuse and cleaning/retightening a connector are basic jobs. Important: an ABS fuse that blows again immediately signals a downstream short circuit to track down (not just a fuse to swap) — which then means a professional. For this reason, and because ABS is a safety system, you can handle a simple fuse/connection issue yourself, but leave the rest to a professional if the fault persists. This is the simplest path to rule out first.

Warning: a safety component (expert-only safety lock). More rarely, it's the ABS control unit itself — the electronic module, often built into the hydraulic modulator — that's at fault. This unit receives the sensor signals, decides when to modulate brake pressure, and drives hydraulic solenoid valves. It's a sealed part that can't be repaired: it's replaced and coded to the bike (configured via the manufacturer's diagnostic tool), and the ABS circuit then needs bleeding. This is the rarest but also the most expensive cause. Diagnosis must absolutely confirm it's really the control unit — and not a sensor, a fuse, or a loose connection mimicking the fault — BEFORE ordering an expensive part. This job (full diagnosis, replacement, coding, bleeding) is entirely a job for an equipped workshop: rated expert-only. The tell that can point here: a permanently lit warning with a fault code pointing to the control unit/module, once sensors, fuse, and wiring are ruled out. On budget, this is the most expensive part in the system (several hundred euros, possibly more), which makes a rigorous diagnosis worthwhile, and possibly a certified reconditioned part. In the meantime, the regular brakes work: ride carefully with no emergency stops, and never permanently disable ABS.

Repair to be left to a professional.