E Class Cruise control

I have an E Class CDI 220 - There is an intermittent fault on the the cruise control which I can't fix. Some days it works faultlessly and other days it won't work at all. It never fails in operation.
Sometimes simply stopping, waiting and then starting againn seems to do the trick. The only fault showing in the brain was a faulty brake light switrch and I have replaed that to no effect. Anyone any ideas please.
Wilby
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How old is the battery. Mine was faulty on my E320 and it would show up as intermittant malfunctions in a variety of different areas, one of which was a cruise control problem every now and then. Replaced the battery, and it all works fine
wilby wrote:

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I've tried this - it doesn't seem to be the problem - but thanks.
Shawn wrote:

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Check that your brake light switch is working correctly. My cruise control had an intermittent failure which the dealership could not resolve (thankfully it was under warranty) until some guy pulled up next to me and said that my brake lights were not working. Sure enough, about one out of every five or 10 times that brake lights were not coming on where I pressed the brake pedal. This short caused the cruise control to not engage.
Josh
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wilby wrote:

codes reported. Like yours it is usually cured by restarting the car. I had thought the problem had been cured when the brake detector switch had its contacts cleaned and lubricated - that certainly cured the other problem which was the shift selector refusing to leave Park - but the problem has reoccurred occasionally since. Now I have a new battery I shall see if that makes a difference.
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I had similar problem and turned out to the sight vibration due to the balancing on my wheels being out. This causing the switch to disengage. However, yours does indicate a faulty brake switch.

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Check the brake light switch, bad contact in the pedal switch is probably the reason, it was the problem in my car.
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Kris De Voecht
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Thanks to all.
The car has a new brake light switch so that problem was eliminated. I have then been back and checked the battery again. It is the original and 6 years old and although it appears OK in normal use the voltage was a little down. I have replaced the battery and the cruise now functions perfectly 100% of the time. The only thing I can think is that as part of the checks carried out before starting a voltage reading is taken and stored, if the voltage indicates a sub standarad battery then the brain refuses to engage the cruise (just a theory).
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