1998 Chrysler Town and Country Repair Question
You mean the switches in the steering wheel? Gotta unbolt the air bag. What's the symptom? Switches don't fail very often.
It has 170k miles and the cruise control lights up but won't set.
Light on the dash comes on, so I'm pretty sure it's working, but the set switch won't work.
Yup. The switches are not the problem. Well, I should qualify that. All of the switches work on just one pair of wires. If the "on / off" switch causes the green "cruise" light on the dash to turn on, you know the wires including the "clock spring" under the steering wheel are okay. Each switch feeds a different voltage to the Engine Computer so it is indeed possible the "set" switch is defective, but the chances of that are very small.
First of all, try holding the brake pedal up with your foot when you press the set button. If that works, the switch is out-of-adjustment or has a bad contact. Next, find the throttle cable on the engine coming from the servo. Tug on that cable. It should pull out maybe half an inch. If it pulls out a lot more, it is broken or disconnected in the servo. That's not too common either.
The best plan is to find someone with a Chrysler DRB3 scanner. Besides the dealer, a lot of independent shops have them because they can be used on many other brands of cars built after 1996. The display will show every switch related to the cruise control and whether they are "pressed" or "released". If you see "Brake pedal: pressed" when it really isn't, the contacts in that part of the switch are pitted. You can test every switch in the system while watching the display.
Next, it will list the "reason for last cutout". Obviously, since you stopped the engine when you got to the shop, the last reason shown will be "ignition switch", meaning it was turned off. If you leave the engine running, the reason will be "speed below minimum threshold" meaning below about 35 mph. The idea is to drive at highway speed, turn the system on, press the "set" button, THEN see which reason is listed.
You can also check for stored diagnostic fault codes. I autopsied a defective servo once and found a broken solder connection. It worked fine once it was repaired, but I found it quickly because the Engine Computer detected it and set the appropriate code. The computer will disable the system because that valve could be the one that vents the vacuum when commanded and if it's not working, the system won't disengage when you tap the brake pedal.
Your comment about holding the brake pedal up when pressing the set button made me think. The cruise control was working last Friday morning. In the afternoon we took the car in to have the brakes fixed. That evening we noticed that the cruise wasn't working. Could they have messed up something while doing the brake job? Shouold I go back to the brake place and have them check it?
Actually, the two should not be related, . . . howEVER, . . . if something was done that required bleeding the air out of the hydraulic system, mechanics will sometimes work the brake pedal by hand to get the process started faster. There are some things that can be done that cause other brake system problems, and to avoid that, the bleeding method that most mechanics use prevents that damage but takes longer. They will work the brake pedal by hand a few times to convince the fluid to start flowing. I guess I could see how pulling the pedal back up could cause the switch to get out-of-adjustment but that would be extremely uncommon.
That switch is self-adjusting. The plunger sticks out too far when the switch is installed when it is new. Releasing the pedal pushes the plunger in to its perfect setting. According to the service manual, that switch can only be adjusted once and if it gets over-adjusted it is supposed to be replaced, but I HAVE been able to pull the plunger out by hand more than once.
Here's a photo from http://www.rockauto.com that shows what the switch looks like. In the top one, the thing on the right that looks like a black plastic nail is the plunger. That piece slides into a second part of the switch to self-adjust. It is under plenty of tension to hold it there so if you try to pull it out a little by hand, you'll have to pull quite hard. I don't know if it will come all the way out as I never pulled one that far, but if it does come out for you, I suspect it can just be popped back in.
I really don't think the people who did the brake work caused the switch to be mis-adjusted, but you can't argue that it would be quite the coincidence for some other cruise control problem to develop at exactly the same time. Before you jump to conclusions though, try holding the pedal up with your foot. If the cruise control will set, we'll know you're in for a simple, quick repair. If the cruise still doesn't set, don't panic. It's possible the brake pedal is all the way back already and hitting a mechanical stop. You might try wrapping some tape around the plunger to hold it in further, then see if the cruise will set, but be aware that will prevent the brake lights from turning on and the cruise will not kick out when you tap the pedal. You'll have to turn it off with the switch on the steering wheel, otherwise they'll find you in the next county still peddling away!
Thanks for all the information! I will try the brake pedal technique you suggested. If that fails, I guess to the shop we go! Thanks for all your time.