Jeep Grand Cherokee cruise control

[drsmile]

So I bought a 04 WJ yesterday as a knock around vehicle. 100k on the odometer and very good condition. Only issue is cruise. Light will turn on when the on/off switch is depressed but it won’t set and hold speed. I know this is run on vacuum, but after having the passenger side headlight out and battery tray out to see and check all vac lines, all lines are good throttle body back to the vacuum canister. AC vents changing sources fine - so I don’t t think it’s a vac leak. Brake switch seems to be working fine, all fuses check out. The actual button on the wheel sees to be ok and making contact correctly (cleaned with CRC).
I’m lost. I cannot find an issue, no codes, nothing. Anyone have thoughts or can point to a shop in E Cobb or Woodstock?

 

[the_great_white]

Is there a relay that activates it somewhere?

 

[drsmile]

Not in the schematic. There is “servo” which is just a diaphragm that the vac works on, then the diaphragm is connected to a cable that goes back to the throttle. I guess the diaphragm could be bad. I hate just throwing new parts on and trouble shooting that way - waste of money bc you end up spending money on parts that may not have been needed

 

[jeep78]

Want to really waste some money? Take it to the dealer!

You can check the diaphragm with a vac source (a mighty vac or even just a length of tube and your mouth).

Those are not often used systems, I would inspect for damage or poor connections under the dash or the steering column.

 

[jeep78]

Also, check ALL your fuses with a multimeter, not just a visual check. You have a speed sensor that is likely coming from the computer, a loose connection there would make it inop but all subsystems would check fine.