How to Fix – Dodge Ram Cummins Cruise Control 8

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:

Dodge Ram Cummins Cruise Control Fix
Vacuum Pump on the inside of the passenger side fender near the firewall.

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.

Dodge Ram Cummins Cruise Control Fix
Testing vacuum pump with a MityVac or other vacuum gauge.

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.

Dodge Ram Cummins Cruise Control Fix
Testing vacuum at the next junction.

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.

Dodge Ram Cummins Cruise Control Fix
Had to remove my fender flare first.
Dodge Ram Cummins Cruise Control Fix
The inner fender is fender only attaches with a handfull of small bolts. It isn’t structural so it can be pulled out without removing anything else.
Dodge Ram Cummins Cruise Control Fix
Here is the flare out. I didn’t have to take the wheel off but you might if your truck doesn’t sit up as high as mine. It is plastic so it flexes pretty easily.

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.

Dodge Ram Cummins Cruise Control Fix
Vacuum control solenoid with vacuum hose already removed.

After pulling the hose I found the hole pretty quickly:

Dodge Ram Cummins Cruise Control Fix
Vacuum hose that has rubbed through causing my cruise control not to work.

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.

Dodge Ram Cummins Cruise Control Fix
Checking our inventory…
Dodge Ram Cummins Cruise Control Fix
New Vacuum hose installed on the solenoid.

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!

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8 thoughts on “How to Fix – Dodge Ram Cummins Cruise Control

  • Lady Deanna and Tombstone Tommy

    THANK YOU VERY MUCH!! I found you on google. I am sure this will fix the problem. Thanks for taking the time for your detailed information and pictures too. Tell Gertrude hi for me. I know she is a great help!! By the way…you come up on the first page on google just a few items down. You must be helping a lot of people like us. God bless.


  • Don Blizard

    Do you know the inner diameter of the vacuum hose used for this? I have a brittle plastic vacuum line which melted, and I don’t think the line is any longer available. Thanks!

    • Paul Post author

      Thanks for the question Don.

      I don’t know the inner diameter of the vacuum hose off the top of my head. I want to say it was 1/4″. What I would do if I were you would be to take the hose off and take it in to the auto parts store. They usually sell vacuum hose by the foot off of big reels and can match up to what you need.

  • Kyle

    YES!!!! I bought my ’04 Dodge Ram 2500 and with the camper on or towing, cruise control would only work on perfectly level, flat, easy ground, and sometimes not even then. Sometimes, the truck’s CC wouldn’t work at all, even empty/unloaded.

    I knew somebody would have posted a possible fix, and sure enough, this did the trick. The rubbed out hole in my line looks identical to yours. I was able to get a slightly larger line, cut out the busted section, sleeve the two (and zip tie for double assurances) together and now the vacuum pump actually shuts off after a few seconds!

    The only difference for me is that I was able to get my arm in from the top – I had to have knees on the bumper, but with some crazy angles, I was able to see the solenoid connection for the hose.

    BTW, the hose was not 1/4″, it was more like 1/8″ exterior diameter – to any others reading the comments.

  • Joseph R Alexander

    That was very straight up of you to post that. I’m a shade tree mechanic at best. I’ve always had gas powered everything. I could normally get myself home. This Cummings might as well come from an alien planet. I know just about enough about it to put the proper fuel in.
    I’m on a delivery took a car from Reno NV to Post Falls ID. Just past Lovelock NV my cruise goes wonky. Now my foot is tired and I think I’m getting shin splints. So now I know at least one thing to check. So thanks.