n2it

I have developed an intermittent problem with my cruise control and would like to know if anyone has had the same experience and what the resolve was for the problem. The cruise can work perfectly one minute and will not engage the next. Usually, and I stress usually, if I turn the car off and re-start, the cruise will work again. In some instances, I have had the cruise on, had to take it off for whatever reason, and then tried to re-engage it and it would not work.

Part two of this scenario is this: my motor and transmission mounts have been going bad and they are at the point that the engine will sometimes shake fairly hard. They are getting replaced tomorrow (dealership, OUCH!). Is it possible that the shaking of the engine is causing the cruise to disengage and not work? I don't know much about cruise control nowadays; does it still have a vacuum line? If so that could certainly be the issue.

Thanks for any input!

Plutoe

Most simple intermittant cruise control issues can be solved with the replacement of the brake light switch. The serious issues are with the switch and or the ECU!!

I doubt that a motor mount issue would impact an issue with the cruise control. Good Luck

n2it

I am aware of those issues as well but was wondering if anyone with bad motor mounts and experiencing bad vibrations as a result also experienced any issues with their cruise control.

After the installation of the motor mounts and new front springs this car is driving like brand new. Hated to pay the dealer cost but it was worth it in the end.

Interestingly enough I had no issue with the cruise control today either...hope it's not a fluke!

n2it

I have not experienced an issue with my cruise control since replacing the motor mounts (knock on wood). I can only figure that the excessive vibration had something to do with the cruise not workiong properly...works like a charm now.

renault12ts

Interesting...the vibration from the bad mounts may have fooled the speed sensors into thinking a wheel was losing grip, and thus knocking off the CC. Try it above 70mph...if there's still a problem, usually it will kick off above that speed.

I assume all your tyres are in good condition...a tyre more worn than the others will also kick it off.

fritza2tt

I too have an intermittent problem with my cruise control and would like to know if anyone has had the same experience and what the resolve was for the problem.
In my case the cruise control will not engage, but once it does engage, it will continue to work perfectly until the engine is stopped. I have had this problem for a long time and it has been the same since it began. I have noticed one thing though, If it is hot outside and really gets hot inside the car, the cruise control will engage most of the time. In the winter time you might as well forget it.
I have examined the inside of the cruise control amplifier, but everything looked normal. So put it together again and everything continued to be the same as before. I disconnected and reconnected the stop light switch (still do not understand how it provides a ground to the cruise control and is able to operate the stop light with but wires connected to it, the body is plastic and seems unable to provide a ground.) I also disconnected and reconnected the c.c. control stalk at the steering wheel.
My conclusion is that that some part in the c.c. amplifier needs to be hot in order to provide the initial ground that turns the C.C. on. Does that mean I will have to replace the C.C. amplifier or is there a way to have it tested and repaired?

Plutoe

This is the W210 forum--your question would be best served in the W124---as most here may think a cc amplifier is apart of the sound system!!

fritza2tt

Plutoe, Sorry, I may have mislabeled the cruise control innards, but the operation basically is the same, and that's what I am interested in.

Plutoe

We do not have the same inards as the W124---the W210 is very streight forward--speedsensors,and sensors that impact speed, the CC switch and ECU---very different than the more complex W124 CC

fritza2tt

All of the things you mention work perfectly in my car, it's the intermittent operation which has me puzzled and which could well be an issue with all cruise controls, since they all disconnect when you hit the brakes and the stop light comes on. The problem must be in this part of the circuit. Today it got really hot outside and the cruise control worked perfectly. Obviously the CC finds a better ground through the stop light switch and then everything works. I bought a new stoplight switch, hooked it up, but the CC did not work. Therefore my old stop light switch must be ok. So now what?

fritza2tt

The cruise control came on regularly when it was hot and preferably also humid outside and would not work at all when it was cold and dry. This pointed to a cruise control ground resistance problem, which corrected itself when the contact area expanded when hot. For the cruise control to engage it has to find a ground through the brake stop light switch and the stop lights themselves. Pulling out the bulbs I noticed that after years of use detents had worn into led contact area on the bulbs. I replaced the bulbs with new ones making firm contact and this seemed to have solved the problem, that is, as long as it is hot summer weather. On cool mornings it was back to the way it was before. :-(
Pictures: 2007ML63 AMG - still drives like new and is in show-room condition.
1987 300D Turbo, fastest Diesel sedan at the time, Top speed 125 mph, still in daily use with 265,000 plus miles onit.

Airman15

My CC issue was a bad wheel speed sensor which actually also affects the auto locking feature when you first drive off.seemed to be a pretty easy fix once diagnosed with a STAR Xentry. Check that your speedo doesn't jump to 10-12km/hr from zero. It should sweep smoothely, that is one way of diagnosing a possibly bad wheel speed sensor