Truck is '06 Pete 387, ISX, Auto Shift tranny. While driving, cruise sets, but then intermittently kicks out. Sometimes it will go hours and be fine. Sometimes it will kick out and refuse to reset for many minutes. Sometimes, turning the headlights on and then back off will cause it to kick out. Seems to have the biggest problem while sitting still and trying to idle the engine up. Generally it will not idle up at all, and when it does, it usually kicks out after just a couple of minutes. Computer shows that brakes are being applied intermittently even though nobody is in the truck. Was told it was the brake light pressure sensor, so I replaced that to no avail. I am about ready to take a sledge hammer to my new truck, or burn it to the ground… you’d think that when you drop $76K on a 200k mile truck you could expect an operational cruise control.. Anybody out there have any ideas?

 

It may also be any wiring connecting the brake switch to the ecm. If you can get it on fast idle wiggle the loom & connectors between the switch & ecm. it may be a connector not full seated, or a pin in the connector damaged etc.......look at everything carefully.

 

Is this truck equipped with the Eaton Vorad system and the Smart Cruise deal? I am assuming not, but if it does have the Smart Cruise system you can override that feature by turning the cruise on and off three times rapidly to put it in default mode.


All these electronics are nice when they work, but tracing a problem like that could take days.

Since you state:
I am thinking you may have a poor ground connection somewhere. Probably too much paint between the frame rail and a ground wire. Places I would check include the ECM and primary fuse/relay box. Make sure they are fully grounded.

I had a issue in my old rusty pickup truck where applying the brakes when towing an electric brake trailer caused my CB radio to cut off. Something about the connection from the body panel where the CB was grounded to the frame could not handle the extra grounding needs of the electric trailer brake controller. Grounding the radio directly to the frame rail with 12 guage wire as well as grounding several other body panels to the frame rail solved the issue. The electrons seek the easiest path to ground and in your case the easiest path may be backwards through the brake pressure sensor. Yeah that is a stretch I know.


You can also check weather the cruise has a fuse or a self resetting circut breaker. If a circut breaker is tripping out from a short it would reset in a few seconds so the cruise could be re-engaged.


In my TMC truck which is a 2006 pete 379 I have one electrical gremlin. During wet weather the return stroke of my windshield wipers causes the idiot light in the airbag deflation switch to flash on. It happens only when it is very wet and everything outside and under the truck is soaking wet.

So I don't think I have helped you, but good luck.

 

sounds like the switch on the brake pedal needs adjusting. Does it happen more when you go over bumps? If it does, try holding whatever pedal causes it to kick off up(brake or clutch) and go over same bumps again, if it's fine, the switch needs adjusting.

 

I had the same problem with my '07 Freightliner.

By Autoshift I assume you mean the three-pedal and not the two-pedal Ultrashift.

My clutch switch was loose, but by your description I almost guarantee your problem is something in the brake switch.

-p.

 

Well, the things worked flawlessly for almost two days, then quit and wouldn't come back. After 2 days, I got it into KW in Salt Lake (nice facility, btw if nobody has ever been there, they have over 40 service bays, and a newer facility) and like most service writers the guy completely disregarded what I told him, so I had to re-explain everything to the tech who came out to the truck after a couple of hours to let me know that they needed to order the brake light pressure sensor (which I told them I had just replaced... duh). $270 and three hours later the cruise is working intermittently like before. The KW gut said they tightened up a main power cable to the fuse box, cleaned some corrosion on some of the fuse contacts and replaced a relay. He said they checked all the wiring and everything looked perfect. He also said that last time they had a truck with a problem like this, they called Peterbilt (I guess KW is lost on 387s) who told them the problem is usually in some sort of control panel located behind the glove box.

Rawlco, I have no idea what a Vorad system is, nor a Smart Cruise. But had thought that that the problem occasionally happening when the lights are turned on and the back off could indicate a ground problem.

allan5oh, the 387 does not have a brake pedal switch like you are thinking of (does have a clutch switch $115, but not the prob). It has a pressure sensor that goes into an air junction box located under the cab on the driver's side.

PhuzzyGnu, you are correct, the Autoshift has a clutch.

I do appreciate everybody's input. I'm probably going to just deal with the problem until money isn't so tight (wife / co-driver has Ovarian cancer and has been home getting chemo ($4k a month) instead of driving & we are in the process of getting our own operating authority after 3.5 years to top it all off. I'm betting on that control thingy behind the glove box. It sounds really expensive, so that is probably the problem.