no high engine brake

[Chamberpains]

I forget, what year and model truck is this in?

I think you said it was a 9400i. But I may be mistaken. The problem you describe sounds exactly like the control module for the turbo actuator malfunctioning. what is the max boost pressure you are getting when you're Jake's are on high? What are they at on stage 2? What is Max boost pressure under throttle when it's malfunctioning? What is Max boost pressure when it's not malfunctioning?

I see you have replaced the control module but just to let you know it is not unheard of for brand new straight out of the box holset actuator control modules to malfunction. I know of two guys in the last year that had this happen to them. I'm not saying that's your problem for sure but if you check everything else and it all checks out okay then this may be a possibility.

It looks like your ECM is commanding the correct commands but the components after that are not responding correctly. If I were you I would step by step go down diagnosing to make sure that circuit is operating correctly. First off you need at least 90 PSI to the module itself. If this is a 9400i, under your driver's side cab there is a treadle valve attached to your brake pedal. The feed line to the control module comes off this treadle valve. there is a pressure reducer attached to the treadle valve itself. This may be plugged or not operating correctly. It is a son of a bitch to get to but simply make sure you have at least 90 to 120 PSI going to the control module. If not your problem resides somewhere in that chain. After that rig up a pressure regulator right after the control module into the airline with some shop air. Then run shop air from 0 psi to 90 PSI over to the actuator itself. Ensure that there is no leaks anywhere in that range. Make sure you have full clean travel of the actuator itself within that pressure range. It is not unheard of for the line that runs from the module over to the actuator to be pinched shut underneath the steel braided line. It is plastic line wrapped in steel braid. Check it out very closely. This circuit is ultra finicky. The slightest restriction will throw everything off. make sure there is zero debris in the tubing anywhere. Blow it out with clean shop air.

I believe you said you replace the harness to this module so that would exclude the wires being old. But it never hurts to ohm them out to ensure they are making proper contact. check the pins to make sure they're not recessed anywhere in the chain. The wires are only about 5 ft long and not hard to run out all the way back to the ECM. Cummins quick-serve also has the specs and a procedure on testing the harness. If you're not on it, it's free to sign up and get all kinds of handy procedures including the one for the harness.