FAQ
TL;DR: Root cause was simple: 1 broken wire to the left-rear ABS sensor. “The break was on the wire to the left rear wheel.” [Elektroda, AZUKS, post #16864638]
Why it matters: This FAQ helps Renault Megane Scenic 1998 owners fix persistent ABS lights without replacing good sensors.
Quick Facts
- The dash re-lit after a few kilometers and only reported a generic rear-sensors fault. [Elektroda, AZUKS, post #16816096]
- Typical rear wheel-speed sensor resistance measured by the OP was >= 1050 Ω. [Elektroda, AZUKS, post #16816096]
- ABS pump connector pin map: LF 3&18, RF 1&17, LR 14&21, RR 5&13. [Elektroda, Daro122, post #16832939]
- A damaged ABS ring/crown can trigger persistent wheel-speed errors. [Elektroda, KrzysiekBTW, post #16844636]
- If the error shows even at standstill, suspect wiring first. [Elektroda, kaza12, post #16839937]
How do I fix a persistent ABS light on a 1998 Renault Megane Scenic after brake work?
Start at the wheel you serviced. Inspect the sensor, ABS ring, and especially the harness to that corner. The forum case ended with a single broken wire to the left-rear sensor being repaired, clearing the fault permanently. “The break was on the wire to the left rear wheel.” [Elektroda, AZUKS, post #16864638]
My scanner only says “rear sensors fault” without left/right—what should I check first?
Check the wiring to both rear sensors. Community guidance shows that ambiguous rear faults often trace to a harness break rather than the sensors. In the documented case, repairing the left-rear sensor wire resolved the persistently returning ABS light. [Elektroda, AZUKS, post #16864638]
Can a leaking rear brake cylinder cause an ABS sensor fault?
Yes, it can contribute indirectly. Focus diagnostic steps on the serviced rear wheel first. Fluid, dust, or mechanical disturbance may affect the sensor or ring. The thread’s advice was clear: “So start from this circle,” meaning the wheel where the cylinder failed. [Elektroda, ALIBABA I, post #16817211]
What are the ABS pump connector pins for each wheel on this model?
Use this map for continuity checks: left front 3 and 18; right front 1 and 17; left rear 14 and 21; right rear 5 and 13. This lets you meter each sensor from the pump plug without guesswork. [Elektroda, Daro122, post #16832939]
How can I tell if my issue is wiring or a bad sensor?
If the fault is present even with the car stationary, check the harness first. A standing fault often indicates open circuit or short, not a speed-detection problem. One expert’s concise verdict here was “wires,” which proved correct in the case. [Elektroda, kaza12, post #16839937]
Scanner shows zero speed from the left-rear wheel while driving—what next?
Meter continuity from the ABS pump pins to the left-rear sensor. If wiring passes, inspect sensor air gap and the ABS ring for damage. The case thread noted the left-rear showed no speed and the fault couldn’t be cleared until wiring was fixed. [Elektroda, AZUKS, post #16832317]
What’s a quick 3-step method to test rear wheel-speed wiring from the ABS pump?
- Unplug the ABS pump and identify LR pins 14 and 21.
- Measure resistance through the LR circuit; compare to the other side.
- If open or erratic, trace and repair the break along the LR harness. [Elektroda, Daro122, post #16832939]
What is an ABS ring (tone wheel) and why does it fail?
It’s a toothed wheel the sensor reads to calculate speed. Corrosion, cracks, or debris increase the gap or break the signal. A damaged ring was highlighted as a must-check item for persistent faults in this platform. [Elektroda, KrzysiekBTW, post #16844636]
What sensor resistance should I expect when testing?
Typical reading reported by the OP was at least 1050 Ω per wheel sensor. Large deviation or an open circuit suggests wiring or sensor failure. Use consistent meter setup and compare left vs. right for clarity. [Elektroda, AZUKS, post #16816096]
Why does the ABS light return after clearing codes and a short drive?
The controller re-runs plausibility checks once the wheels turn. If a wheel provides no or inconsistent signal, the fault re-sets. In the thread, the light reappeared after a few kilometers due to a broken left-rear sensor wire. [Elektroda, AZUKS, post #16816096]
I can’t delete the ABS error even at a stop—what does that imply?
A non-clearable fault at standstill points to a hard failure, usually wiring or connector damage. In this case, repair of the left-rear sensor wire finally allowed the code to clear and stay off. [Elektroda, AZUKS, post #16839856]
How do I identify pin numbers on the ABS plug without labels?
Disassemble the connector shell. The numbering is molded into the plastic inside. One expert tip: “Undress the plug and you will find descriptions.” That enables accurate continuity tests per wheel. [Elektroda, Daro122, post #16840271]
Could cleaning sensors and rings be enough to fix the issue?
Cleaning helps if debris or fluid contamination caused weak signals. However, if the fault persists at rest, inspect wiring. The OP cleaned both sides, yet only repairing the left-rear wire solved the returning light. [Elektroda, AZUKS, post #16832317]
What is a wheel-speed sensor and how does the gap affect it?
It’s a magnetic pickup that detects ring teeth passing by. Too large an air gap or a damaged core prevents signal generation. As one expert wrote, failures come from a “damaged sensor core” or excessive gap. [Elektroda, diablo23248, post #16834398]
Edge case: my tool is old and shows only generic rear faults—how do I localize?
Use live data for each wheel’s speed while driving slowly. The dead channel reveals the corner. The thread used an older scanner, saw no left-rear speed, then confirmed and repaired the left-rear harness. [Elektroda, AZUKS, post #16832317]
