Cruise control on your Cummins powered diesel Dodge Ram not working? Read more to see if this article might help you fix your problem.
So I know this isn’t fabrication but if I had to do research, and repair it then I know that a lot of you out there are having the same problem too.
My symptom was that the cruise control didn’t work at all. The light on the gauge cluster lit up green ‘cruise’ but didn’t actually do anything. I have read that some others had issues with the cruise control engaging but not holding speed.
After doing some research, I learned that the cruise control on these diesel trucks are controlled by vacuum. Diesels don’t naturally create vacuum (because they don’t have throttle plates, speed is controlled by the amount of diesel that is injected) so these Dodge Ram Cummins trucks (2003 and newer) have an electric vacuum pump on the inside of the passenger side fender near the firewall. Looks like this:
So next step was to turn the ignition to the ‘on’ position and listen to the vacuum pump. I could hear mine running but it would not shut off. I pulled the vacuum hose off the bottom and plugged the hole with my finger and it shut off within a couple of seconds. If you can’t hear yours run or it doesn’t shut off when you plug the hole then you might need a new vacuum pump.
Vacuum pumps for this truck can be had for pretty cheap on Amazon at the link below:
There is a slightly more scientific way to test it than putting your finger over the suction hole. I used a MityVac that I had in the garage. These are also pretty cheap and handy. Other than this purpose, MityVacs can also be used for bleeding brakes and testing anything else that might have or require vacuum.
These are just handy to have around the shop if you do much automotive work:
First I tested it up by the vacuum pump where it showed ~15″ of vacuum. The next test was at a junction on the drivers side by the firewall where it also drew 15″ of vacuum.
After knowing that the hose was good up to this point, I tested the other side of the junction where I couldn’t draw any vacuum with my Mity Vac no matter how fast I pumped. So I knew my problem was between the junction and the cruise control solenoid under the drivers side battery.
I couldn’t get to the cruise control solenoid and I read that it is easier to go through the wheel well than take out the battery. So next step was to remove the fender flare then inner fender.
Looking up from inside the fender, you can see the cruise control module. In this picture, I had already removed the vacuum hose so I could do another vacuum test on it, in which it failed. So I now know the problem is with the hose between the solenoid and the junction.
After pulling the hose I found the hole pretty quickly:
So after realizing that it was an easy fix, Gertude and I went over to the ‘Bulk Hose’ bin to see if we had any vacuum hose of the right size to get it fixed up.
Before putting the inner fender back on, I turned the ignition to the ‘on’ position and listened for the vacuum pump to turn off. Sure enough it turned off after about 3 second of pumping and I knew that all was good and I was ready to reassemble.
Took Big Blue out for a test drive and the cruise control now works like a champ. My apologies for this not being related to metal fabrication or welding, but it is very much DIY. I did this myself in an afternoon and YOU CAN TOO. So save yourself some money and go out to the shop. If you fail, Google and blogs like this are there to help you out!