Case/011

Volkswagen Golf Mk7

ABS and ESP lights after wet weather

Cause: Corroded connector on the rear-left wheel-speed sensor letting water bridge the terminals.
Outcome: Connector and pigtail repaired to manufacturer specification, signal re-checked wet and dry. Lights have not returned.

Customer report
The lights came on only after driving in rain, and always went out by themselves. The customer wanted to know if the car was safe and whether the whole ABS unit needed replacing as suggested.
Initial data
A stored code for the rear-left wheel-speed sensor showing implausible signal, logged intermittently. The sensor itself read correctly at the time of the scan.
Testing
Each sensor was scoped at road speed on the lift to compare signal shape. All four were clean when dry. Spraying the rear-left hub area produced signal dropouts within seconds; the other three stayed clean.
Cause
Green corrosion inside the sensor connector. Water gave it a path to short the signal, which cleared as it dried.
Resolution
New pigtail soldered and sealed, connector replaced. Signal re-tested wet and dry with no dropouts. No ABS unit needed.

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