Mercedes-Benz W140 cruise control not working
350 TD320 SS 420300 SE
Why does the W140 cruise control not engage or not stay on?
Check the brake light switch first. If that does not help, the fault is often in the cruise control unit, whose solder joints or dried-out capacitors are bad. A used control unit has fixed the function.
Where is the cruise control unit?
The unit is above the driver's left knee behind the plastic covers.
Can the tyres or the speed sensor prevent the cruise control from working?
Yes. Different-sized tyres on the front and rear axles can limit operation to low speeds; same-sized tyres fix the problem. The speed signal comes from the left front wheel ABS sensor, and oxidation in the wiring can interrupt the signal. Repairing the sensor is a job for a workshop.
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