Cummins engine brake acting weird

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Z

ZinLuvR

Well-known member
Joined
Jan 23, 2018
Posts
129
Location
Colville, WA
This one has me.  Just started.  Seems like the engine brake is not coming on at times, and then at other times it seems to come on with the switch in the off position.  When in off and I let up to coast I feel the engine brake come on, or, I also notice at the same time the trans has gone to 3rd gear, Allison 4000.  So I'm not sure if the TCM might be causing a downshift when I let off the gas or the engine brake has come on.  I'm almost thinking it's the TCM since I don't remember seeing the trans go to 3rd when using the lo engine brake before.  Also, this is the first time with the toad hooked up.  Electrical issue with the umbilical cord?  Feed back loop from the toad to the TCM?  Bad rocker switch?  Not sure where to start.  Tomorrow I'll disconnect the toad and go out and find some hills to see what happens.  But it seems like the engine brake when in "lo" wouldn't cause the trans to go to 3rd, or does it?  Thanks.
 
I would think it would be an engine brake (two stage, perhaps?) Ours has an indicator light on the instrument panel that illuminates whenever the Jake is engaged. Do you have such a light? If so, is it illuminating when the switch is off? Our coach's brake lights also illuminate when the Jake is engaged. Do yours?

I'm sitting here trying to think how an interruption in the brakelight circuit, caused by the towed vehicle's brakelight wiring, could cause such a problem, but off the top of my head, I can't. It'll be interesting to hear if driving without the toad makes any difference.

Kev 

Edit: I just noticed that it is indeed a new towed vehicle setup. Now I'm really interested in learning if the issue continues without the toad. Whenever I encounter a problem after working on something, I undo what I did to see if that fixes the problem. It seems like, more often than not, what I did caused the problem.
 
Engine brake, shuts off 3 cylinders on lo.  Didn't get a chance to take it out without the toad to test.  New problem.  The toad battery was completely dead this morning even though I disconnected the power from the coach, but did leave the toad trans in neutral.  Strange.  Will be back on the hunt tomorrow.
 
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