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Q: Problem with the cruise control

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My car has 110,000 miles on it. The cruise control is malfunctioning. When I drive at higher speeds like 75 mph, with the cruise control on, the car brake becomes very hard to press as it the engine shut off. If I apply the brake pedal to the limit, the speed would decrease. Also, the brakes would start working normally if I first press it once very hard and then press it as usual. While I'm driving at the same speed, with the cruise control off, everything works great. The dealer thought it was a problem with the brake pedal switch but it wasn't. My car has a CVT. I also noticed that tachometer is not working. What could cause this?

Hey there, thanks for writing in about your 2005 Mercury Montego. Mercury has a technical service bulletin out for brake light switch being either faulty or not adjusted properly causing all kinds of cruise control issues.

The brake lamp switch and brake lamp circuit should be checked. The instrument cluster control unit should be evaluated to be sure it is receiving the engine speed information from the powertrain control module. This information is used to control the tachometer. If you need help having this looked at, you may want to enlist the help of a mechanic, such as one from YourMechanic, who will have the tools and technical expertise to diagnose and correct both the cruise control and tachometer issues.

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