Cummins ISX Engine Break, Cruise Control and Fan Clutch Problems

Check your clutch pedal to make sure it is up all the way and not stuck partially down to constantly be canceling the cruise/engine brake. You fan solenoid may be plumbed wrong for normally open or normally closed depended on what it needs.

 

Normally the fan is engaged with key off. The solenoid is controlled by the ecm which applies power to the solenoid allowing air pressure to disengage the clutch.

If the fan is running full time and the clutch or air line doesnt have an air leak then either the ecm isnt sending power, a wire is broken, the solenoid is defective, or the solenoid is plumbed incorrectly.

If you have the optional dash fan switch it's possible the switch is defective or the body controller thinks the switch is on and telling the ecm to engage the fan.... that's a real fun can of worms.

One other thing i forgot all about. Air conditioning high pressure switch can also tell the body controller to send the ecm a fan on signal.

Confused yet?

 

I'm pretty sure that truck uses a trinary switch rather than separate switches. Regardless, low pressure has no effect on fan operation, only high pressure. However I think you're chasing a ghost going down that route. I'll tell you exactly what I would do to isolate the problem.

First, with the truck off I would jumper the solenoid to verify the clutch disengages properly. Simply unplug from the harness and supply power and ground. If you have air pressure and the solenoid is plumbed correctly it should disengage. If it doesnt, make sure air is actually reaching the clutch.

If that works make absolutely certain both plugs, harness and solenoid are in good condition. No melted plastic or corrosion. Start the truck with the solenoid unplugged and use an LED test light to check the harness connector for power. If there is no power you've found the first clue. Check the other pin for ground. No ground is a big clue. If either is missing the fan will never disengage.

Until you know the answers to the above looking anywhere else is going on an Easter egg hunt. You may eventually find the problem but you're likely to spend way more time than needed.

I'll check back soon in case you post more info or have questions.

 

Very common Cascadia problem. Change your a/c high pressure switch. It is the larger one with the green connector on the passenger side near top corner of radiator. Use 9/16 wrench to remove. You do not need to remove freon from system. 2 minute fix. Google MEI#1324 to see pic. P.S. Look inside connector for loose pins when you unplug switch.

 

If you've done the electrical tests and cant find any wire damage, etc. I'd start looking for a ship with cummins insite software to determine what's telling the ecm to run the fan.