Exhaust Brake

[KIX]

My Jacobs exhaust brake has quit working. Here are the items I have checked and verified that they work but still have no exhaust brake.

Air solenoid opens and closes and passes air on the bench.
Air supply to solenoid is available
Butterfly moves freely with air cylinder disconnected
Air actuating cylinder works with external air applied
Dash on/off switch works as verified by VOM

Road tested at 60 mph and no exhaust brake. Trans downshifts like it should. Wherever the air solenoid gets it's actuation signal is not providing that signal.
Ideas will be appreciated. Thanks

[Ray,IN]

I'm not much on this but have an idea. When the accelerator is released it activates the E brake. Could that be involved in this? Seems like that is sending a signal to something.

[dennis45]

Originally Posted by KIX

My Jacobs exhaust brake has quit working. Here are the items I have checked and verified that they work but still have no exhaust brake.

Air solenoid opens and closes and passes air on the bench.
Air supply to solenoid is available
Butterfly moves freely with air cylinder disconnected
Air actuating cylinder works with external air applied
Dash on/off switch works as verified by VOM

Road tested at 60 mph and no exhaust brake. Trans downshifts like it should. Wherever the air solenoid gets it's actuation signal is not providing that signal.
Ideas will be appreciated. Thanks

Any noticeable difference when you slow down to say 50?

[PandK]

Have you tried putting a close signal on the on/off switch in the dash and checking operation of the solenoid? Possibly a bad connection somewhere between the dash and engine. Think you have the VMSPC - if so do you see the signal indicating the exhaust brake should operate?

[Bigd9]

On an older coach, I found an answer to the same problem as yours to be a plug in the engine wiring harness. I had to trace the wire that activates the solenoid all the way back to a wire bundle and inside that bundle I found a bad plug.

[KIX]

Originally Posted by Ray,IN

I'm not much on this but have an idea. When the accelerator is released it activates the E brake. Could that be involved in this? Seems like that is sending a signal to something.

It does indeed send a signal. Per Spartan the signal is generated by the ECM. And that signal is apparently being generated by the ECM as designed as the signal to downshift the trans is reaching the trans. But there is aparently a loss of signal between the ECM and the air solenoid.

[KIX]

Originally Posted by dennis45

Any noticeable difference when you slow down to say 50?

Dennis, No. I've had this coach for 10 years and about 65000 miles so I'm sure the exhaust brake is not being activated.

[KIX]

Originally Posted by PandK

Have you tried putting a close signal on the on/off switch in the dash and checking operation of the solenoid? Possibly a bad connection somewhere between the dash and engine. Think you have the VMSPC - if so do you see the signal indicating the exhaust brake should operate?

From discussing this with Spartan the dash switch "activates" a "module" in the ECM that in turn controls the air solenoid. So because any external signal I put on the dash switch wiring would pass into the ECM I have been reluctant to do this. I don't want to cause a second problem.
I agree with your thought that it's a bad connection between dash and the air solenoid. So far I have been unable to even find connectors. They're supposed to be in the pax side frame rail over rear axle........they're definitely not there or even close to there.

[KIX]

Originally Posted by Bigd9

On an older coach, I found an answer to the same problem as yours to be a plug in the engine wiring harness. I had to trace the wire that activates the solenoid all the way back to a wire bundle and inside that bundle I found a bad plug.

I feel pretty certain that my problem will be along the same lines. I am hoping someone will have the same chassis/engine and at least be able to tell me where the connector is located.

[dennis45]

Originally Posted by KIX

It does indeed send a signal. Per Spartan the signal is generated by the ECM. And that signal is apparently being generated by the ECM as designed as the signal to downshift the trans is reaching the trans. But there is aparently a loss of signal between the ECM and the air solenoid.

Poor connection or bad solenoid? Since you know the cylinder moves the butterfly on your bench test, try disconnecting the air supply at the cylinder and activate the dash switch with the engine at idle. This should tell you if the solenoid is opening.
You might have to have a helper as I think the transmission needs to be in D, brake applied. Went this route a few years ago when mine quit. Turned out it was a bad connection at the solenoid plug. A good cleaning with electric a spray cleaner and some dielectric grease and away it went.
The solenoid on mine is located on top of the transmission right in the dirtiest spot they could find.

[KIX]

Originally Posted by dennis45

Poor connection or bad solenoid? Since you know the cylinder moves the butterfly on your bench test, try disconnecting the air supply at the cylinder and activate the dash switch with the engine at idle. This should tell you if the solenoid is opening.
You might have to have a helper as I think the transmission needs to be in D, brake applied. Went this route a few years ago when mine quit. Turned out it was a bad connection at the solenoid plug. A good cleaning with electric a spray cleaner and some dielectric grease and away it went.
The solenoid on mine is located on top of the transmission right in the dirtiest spot they could find.

Thanks Dennis. I took the air solenoid out and bench tested......it's good on the bench. I cleaned the solenoid connector, reinstalled the solenoid and road tested. Still no exhaust brake.
Regarding your comment about testing the solenoid operation. On my coach ...........there is always air available at the solenoid inlet. The solenoid is controlled by the ECM and will not open below "x" speed. There is 2 ways to check operation. 1. Visually look at air actuator/butterfly operator or 2. Pay Cummins to connect their software. Cummins can check operation using their software while coach is stopped. Agaoin, that's my coach and per Spartan.
I still think my problem is a bad connector..........just have to find the engine to mid chassis connector.

[Darrel]

For what it's worth on my unit there some components in the Bussman box that are labeled as "Auxilliary Brake". R10 looks to be the relay that is energized from the ECM. Fuse F17 looks to be in the circuit that activates the brake lights if the relay R10 is picked.
This information is from the Spartan wiring diagrams for my RV. It is fiendishly difficult to decipher that information but on my unit each wire is labled according to the diagram.

Have a nice day - Darrel

[KIX]

Originally Posted by Darrel

For what it's worth on my unit there some components in the Bussman box that are labeled as "Auxilliary Brake". R10 looks to be the relay that is energized from the ECM. Fuse F17 looks to be in the circuit that activates the brake lights if the relay R10 is picked.
This information is from the Spartan wiring diagrams for my RV. It is fiendishly difficult to decipher that information but on my unit each wire is labled according to the diagram.

Have a nice day - Darrel

Thanks Darrel. With Spartan's help we determined that everything in the Bussman box is good to go. According to Spartan I'm down to a connector that connects the engine harness to the mid-frame harness.........sure do wish I could find it.

[Darrel]

Kix - I am very interested in your problem since my RV has it also. I have only diagnosed my actuator at the exhaust pipe which was good. I wonder if you could narrow it down to the wiring from Bussman to solenoid or ECM to Bussman. If you could see if the brake lites are activated by the exhaust brake switch you could eliminate the ECM to Bussman portion.

Keep working, I'me rooting for you - Darrel