Jake brake help on 2003 ISL400 Dynasty

[r3meyer]

Need a little help trying to trouble shoot a jake brake issue. Just did a 1000 mile trip and figured out real quick that the coaches jake (low or high) are not engaging. The coach will snowball down the hill if you don't hit the brakes.

What I have done so far.
I replaced the foot switch with a standard toggle switch. It was bad. Now the transmission will downshift when active. I have confirmed 12v across the board. I assume this part of the system is working because it will kick it out of cruise also.

I have test jumped both jake solenoids with 12v and I can hear both clicking.

What I dont get is the wire diagram for the high/low.

Anyone help guide me though this?

[Skip426]

With the trans controller getting the signal to start the downshift program , then one would assume the Cummins ECM is getting the signal too , then your issue is between the ECM and the control system leading to the cylinder head or in the head control solenoids for the hydraulic portion of the system.
Have you been able to check the Cummins ECM for fault codes ?
Do you have the wiring diagram as a pdf ?
Can you post it here ?

[1doodadd]

Will this help??

https://autocardesign.org/cummins-ja...iring-diagram/

[r3meyer]

Whats weird is before I knew the foot switch was bad, if I put the HI/LOW switch into high (pushed fwd) it would make the transmission do the downshifting program anytime the accelerator was not pressed.

I am going to hook up 2 test meters to both solenoid leads back in the engine bay and see if I get 12v on either side.

From what I can tell it take the 12 power right from the jake on switch and sends it right into the transmission harness. the High low just patches 12 into the 2nd jake leg when active.

[TR4]

Just a thought, my ISL deactivates the compression brake when it’s under 10 mph. Maybe it’s not getting a signal from the tail shaft.

Bill

[r3meyer]

Originally Posted by TR4

Just a thought, my ISL deactivates the compression brake when it’s under 10 mph. Maybe it’s not getting a signal from the tail shaft.

Bill

Can you elaborate on what you mean by "Tail Shaft"? What I also just realized is that my ATC led is also on 100% of the time. This is a new coach to me so I am trying to figure out what is working and what is not.

[Skip426]

Tail shaft would be the "output speed sensor "on the transmission , close by the first drive shaft U joint .

ATC ( Auto Traction Control ) could over ride compression brake function .

I'll see if I can dig anything up.

[r3meyer]

Originally Posted by Skip426

Tail shaft would be the "output speed sensor "on the transmission , close by the first drive shaft U joint .

ATC ( Auto Traction Control ) could over ride compression brake function .

I'll see if I can dig anything up.

That would be great. Could be two different issues, but still needs to be resolved.

[Skip426]

I'd have to ask you to update your signature line

Every time I see your old coach listed , I react that the 8.3 didn't have a compression brake.

Question about your coach ATC system , what chassis is your coach on ?
Roadmaster ?

[r3meyer]

Originally Posted by Skip426

I'd have to ask you to update your signature line

Every time I see your old coach listed , I react that the 8.3 didn't have a compression brake.

Question about your coach ATC system , what chassis is your coach on ?
Roadmaster ?

Roadmaster with Tag. I updated my sig.

[Skip426]

I found this thread with some info on the ATC light , have to read all the posts as other info spread through the thread.


http://www.irv2.com/forums/f115/atc-...or-252081.html

Still not sure if the ATC being active would override the compression brake.
But there appears to be info on how to get the light off.

But it would make sense , that if wheel slip was detected , ATC would try to stop slipping and if overriding compression brake was part of that, it would .

[r3meyer]

Ok so I had a friend come over and drive the coach while I worked on a couple tests in the engine bay from up above.

1. I am 100% not getting 12v to either solenoids when the jake is active. I unplugged both wires at the valve cover and checked for voltage when the engine was down shifting and neither side showed any voltage.

2. I unplugged each connection at that valve cover side and while the engine was downshifting energized the solenoids individually with 12v and you could feel and hear the engine brake working.

I can't help but think this ATC light being on is messing with the ECM somehow and keeping it from engaging.

Anyone have any ideas?

[shootist]

Iirc there is a atc fuse in the front run box. Pull it and see if your jake returns. And yes one lead from the ecm runs both halves of the jake. It has a breakout rt front of the valve cover that runs to the front hi/lo switch through the hillam harness. The two wires from the ecm are actually split from one in the ecm.

[r3meyer]

Originally Posted by shootist

Iirc there is a atc fuse in the front run box. Pull it and see if your jake returns. And yes one lead from the ecm runs both halves of the jake. It has a breakout rt front of the valve cover that runs to the front hi/lo switch through the hillam harness. The two wires from the ecm are actually split from one in the ecm.

I will give that a try. Thanks!