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Is a fault in the brake light switch causing cruise control problems in my Volvo S80?

My Volvo S80 has about 114,000 miles on the clock. Recently the cruise control started dropping out for no apparent reason. The "Cruise" indicator light comes on and stays on whenever the system is turned on. There are no error messages. Sometimes it will activate if I hit the Set button again, sometimes if I turn the system off and back on it will work again, it's sort of hit or miss. There is only one switch on the brake pedal. I know this operates the brake lights, does it also have contacts for the cruise circuit?

Asked on 24 August 2010 by dnfrick

Answered by Honest John
Yes, brake light switches are used to 'tell' the ECU and hence the fuel injection system that the brakes are on, and if there is a fault they will give the wrong message. This can be caused by something as daft as a bit of moisture causing a short in the rear light clusters.
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