I am a first time owner of a 2004 Ram 5.9 cummins, I purchased in Oct. I just experienced a bunch of problems with APP sensor which I was able to resolve. Now I have come across something I have never seen before, hopefully someone has! my cruise control is working while the truck is in park. If you turn it on the cruise light comes on the dash then hit set and accelerate it does hit coast and it slows down hit cancel or step on the brake and it goes off. anyone have any ideas??? In my experience the cruise works off the speed sensor and shouldnt work unless going over 30mph.

 

AKA High idle

 

Not high idle, The truck idles around 750rpm, in park you can turn the cruise on and idle it up to 2k rpms with the steering wheel controls and everything in between. hit cancel and it goes back to idle at 750

 

Yeah It is a high idle function. Had the dealer turn mine on also.

 

can you elaborate on that a little?

 

I have a 04 as well and my "high idle" isn't turn on by the dealer, but when the weather outside is in the 30's my truck with automatically kick the RPM up to 1000. The high idle function is there to help keep you truck up at temp and help it get there faster on cold start up mornings. This should be in your owners manual or look up what the high idle is on line. I hope I have helped and I'm sure the dudes on here will explain it much better than I can.

 

The trucks with the auto transmissions can have a manual fast idle option enabled at the dealer...it is controlled by using the cruise control switches/buttons. What you describe is normal. It can also be done with a manual truck, but requires enabling the "PTO" function and installing a switch.

And further, the automatic fast idle that occurs at cold temperatures is to keep the cylinders warm enough to prevent cylinder wash down. This is caused by the unburnt fuel from cold cylinder temps washing the lubricating oil off the cylinder walls. This results in cylinder scoring and broken rings.