My r3efined test showed that the issue only exists when cc is trying to accelerate. Like up a hill or resuming to a speed higher than current vehicle speed. It isn’t cc. It is vacuum. But, the service manager at my home dealership is deluded into believing vacuum is not involved. I would dearly like to get this fixed. I don’t drive a lot, but mostly on the highway. Yesterday evening, I had a near incident. Some twit came down the acceleration lane forcing a semi to move to the passing lane. Two cars and mine behind the semi. Getting off cruise was really important.
I just can’t understand what the rocket science part is where I get that there is nothing wrong and it is working properly. Next nearest dealership is 50 miles away. I guess I can go there and sit for eight hours and be told it is in my imagination. Somebody suggested the next level above the service manager. I forgot who that was. I am also not sure how to contact that person.
Way too much reliance on OBD. Like Tom and Ray have said many times in reference to a chocke, maybe I need a mechanic who is missing a few teeth.
The cruise control is turned off by the brake light switch. In some cases, teh brake light switch has 4 wires, two for the lights and two for the cruise control. Also in some cases, the two wires that turn off the cruise control also control the center brake light. I don’t know how your is configured, but first I’d check the operation of the brake lights, then check the electrical circuit from the brake light switch to the cruise control module.
I want to modify my earlier statement . Your cruise control is working properly except it is not disengaging when you step on the brake. You have a problem with your brake booster or low vacuum.
Does your cruise control disengage the throttle when you step on the brake? If it is not doing that, any idiot should be able to tell that, even if they work at a dealership.
It sounds to me the service manager at the dealership is out in left field. It is pretty obvious that the issue you are having is due to a vacuum problem and he has no clue. I’m not sure why you continue dealing with them on this. I assume there isn’t a warranty issue here and don’t see why you don’t take this problem to a better shop to have it looked at. I also suggest you install a vacuum gauge, even it is just temporary, so you can monitor the vacuum. If there is a vacuum reservoir for the system make sure it is working correctly.
With cruise engaged and vehicle at set speed and heading down a grade, brake pedal works as always. When either heading up a grade or attempting to gain speed after “resume” is pressed, brake pedal is hard to move. Push enough and it moves slightly. As soon as it moves, cruise drops out and brake pedal is fine again.
Nearest next dealer is 50 miles away. I am not looking forward to sitting in a waiting room several hours. Response will be a) we found the issue and fixed it, b) we found the issue but parts had to be ordered, come back, c) we could not reproduce the issue. A bit of a gamble. I would not have thought the problem would have been so complicated for a dealership to diagnose. It is not “new” technology.
I am slowly coming to the realization that another dealership may be the only choice.
I have a vacuum gauge. I have not used it in 40 years. I am not even sure where vacuum lines are on the Montego. They were not obvious, at least not like on other cars (older) that I have seen. An interesting test would be to check engine vacuum while car is driven. But, I have no idea where vacuum inside the car would be. Lots of panels covering things.
Don’t bother looking inside the car.
You need to hook the gauge up to the intake manifold. Or, if you’re feeling brave, tee into the vacuum hose for the brake booster.
Once you’re hooked up, attach the vacuum gauge to the windshield with duct tape and drive the car.
OK, The cruise control is a red herring. If you are stepping on the gas or the cruise control is, the vacuum drops and the brake pedal gets hard.
If you lift off on the gas or the cruise does (because you are going downhill) the vacuum goes up and the brakes work normally)
It is normal for vacuum to drop when you step on the gas and climb when you let off. It is not supposed to drop low enough to affect your brakes.
Fix your vacuum problem and your cruise and brakes will work just fine.
Don;t you have any local mechanics? There is no reason to use a dealership for this.
Were you able to confirm whether the car is actually drive-by-wire? If so, then it won’t be using a vacuum actuator to run the cruise control, so that eliminates that suspect. Drive-by-wire simplifies the design of cruise control, stability control, and traction control, but it is a bugger to diagnose when it fails.
The description is a little confusing because some posts discuss a brake that is hard to push and others describe a cruise control that is not disengaging. Are both things happening at different times? Try just tapping the brake, not enough to slow down but enough to flash the brake lights and disengage the CC. That may eliminate one suspect.
The suggestion to check the brake lights to see if the new switch is good is not necessarily valid because the switch likely has four contacts, so the cruise control disengage function can fail while the brake lights still illuminate. A brake pedal switch for this car is only $10, so trying another one would not be expensive. I would normally suspect the wire between the brake pedal switch and the control unit, but that would not fit well with your uphill-downhill experience.
You don’t need a dealer service shop to fix this problem. Any good shop should be able to fix the trouble. You just need someone who understands how the trouble is happening which is with the vacuum system. If there is a vacuum reservoir it should be checked for proper operation as it is supposed to supply vacuum while the engine is under a big load and the throttle is open wide.