I have this problem with my cruise control. on the way home from work i set it at about 50 MPH. I have to go over a bridge and at the top of the bridge the cruise control shuts off by it's self. any ideas?

the cruise can shut off from many things. bad PMD will cause the cruise to not work at all for some reason. another thing could be the brake pedal switch, so when you step on the brake cruise is suspended until you hit R/A on the switch. could be a bad brake switch, Aces had this issue and had to replace the switch before he could get his cruise to work correctly.

Same thing happen to me it would just shut off then try a few minuts later and it would work again.
I put my PMD under my bumper with a 6' Harness on a heat sink and I naver had a problem since. And the truck runs better too.

http://www.dieselplace.com/forum/garageimage.php?do=thumb&p=65125

x2 pmd

I found that pmd failing will shut off cruise. pull over,shut down for a minute then restart and cruise works again. there is a p1026? code tripped, but the ecm doesnt "see" it upon restart. something about injection event timed too long or short. the code will only be there if you are reading the ecm when the event happens.

PMD is fairly new and already relocated behind the front bumper so i guess i'll look elsewhere. Thanks

Hey Will... is there a bump around the time the cruise shuts off? Does it shut off there every time? Are there other places where it shuts off?

Looking for a pattern...

PMD is fairly new and already relocated behind the front bumper so i guess i'll look elsewhere. Thanks

It dont hurt to try shutting down, takes only a minute, if the cruise comes right back, you have a faulty pmd. If not, then you know for sure. I always try the easiest and cheapest diagnostics first.:confuzeld

At work we had an excursion with a 7.3 that would shut itself off if it lost a certain amount of speed on a hill before it caught it, or if it couldn't keep up. Anyone know if the 6.5's have something like that?

well... seems like the cruise control works fine while going up a hill but after cresting the hill and start going down hill it will always shut off. i'm thinking it has something to do with when the engine does not have a load on it or when the engine is kind of coasting or letting off the fuel, if you know what i mean.

when i use to use the turn signals to the right to change lanes it would shut off the cruise control. i replaced the when i did my tm install it worked it self out. probably not helpful I would check the switch it self have read alot of people with this problem and the pmd was one if that did not fix it then I would look at the switch it self and that would involve the steering column being taken apart. You could always use a brick and a rope !!!!:lol:

OBD-I.... optical sensor filter harness maybe?
Lossing speed on hill and CC shuts off?
Fuel supply issues that causes the optical sensor to have a momentary "mini-stroke?"

There are 3 reasons for the cruise to cut out...

a] touching the brake pedal - the cruise control is an 'on until off' circuit... once you set it, as long as you don't interrupt it, it stays on. Touching the brake pedal breaks that circuit and it's off until you hit resume.
- bad switch on the pedal
- short in wiring to/from switch
- incidentally, this same switch (the one that opens this circuit) is the switch that opens the TCC circuit and forces your transmission to drop out of lock.

b] Any error code will interrupt Cruise... the cruise control on these fly-by-wire trucks is controlled by the PCM, and if there is an error condition, the PCM will go to 'safe mode' and drop things like cruise control. The cruise cannot be resumed until the PCM decides that everything is OK again.
-this is why people are mentioning PMD. A failing PMC will cause an injection 'event', whereby the IP quits for just a second. One glitch is OK, two is getting dicey, and if the PMD sees a certain threshold number of failures in a certain time span, it will set a code and default to safe mode, killing the cruise. PMD-induced failures need to have the truck re-started to re-initialize the PCM before the cruise can be started again... there is no resume from a PMD-induced failure event without restart.
- other code conditions can cause the cruise to drop offline also, but these conditions, once they stop happening, can allow the PCM to re-initialize on the fly, so the cruise can be resumed. If you want to see what happened, you need a code reader to look for history codes, because the codes will not be active anymore.

c] As mentioned, shorts in the switch wiring on the stalk (signal light lever or steering column) can be problematic for cruise control. Again, anything that interrupts that circuit causes the cruise to drop offline. Switch-initiated problems can usually be resumed, once the issue is resolved, so if it's a broken wire that only opens the cirtcuit when the left signal is on, if you shut off the signal then you can resume.

Finally, there is always the loose nut behind the wheel problem... the guy with 'happy feet' that bumps the brake pedal with his feet and can't figure out what happened... you ain't one of them, are yuh?

Details, man, we need details. If you can tell us a bit more about how this issue behaves, perhaps we can collectively come up with some ideas to help.

In what situations does it happen? (look for patterns)
Can it be resumed? (rules out some things)
Does anything else quit when the cruise quits? (ie TCC)
Have you read all your codes? (with a code reader... I know the light isn't on)

JI, I think you just solved my issue for me with your post. I do get a code because i have a TM and a 10K pot installed. for some reason i'm getting a code from the berometer and now that i think of it after the code pops the cruise cont. shuts off. i have not tried to reset the cruise because soon after it shuts off i exit the freeway.

A heath Maxitorque will fix that. Your truck is OBD1 easy install. Will solve the need for boost fooler. Truck will run and shift better too. Worth the money IMO. Didn't do my 2000 because OBD2 and can be PIA to relearn from what I have read. My OBD1 no issues.