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Troubleshooting Jake Brake issues.

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Bought a new to me coach in Feb of this year.  We do a lot of weekend trips and my normal route is pretty flat.  This April we took a trip to Moab and quickly learned that my coaches Jake brake is not engaging.  The coach would snowball down the hills.

Here is what I have done so far.

  • When I first got the coach it would not downshift at all when I pushed on the footswitch.  I found the foot switch was bad and not passing 12v through it.  Had this same issue on my 98 windsor.  I replaced the foot switch with the arm rest switch which I like better and was now getting 12v through the switch.  Still no engine or transmission downshifting.
  • I found the 2 wire connector leading to the HIGH / LOW switch was disconnected when I removed the service panel on the arm rest console.  I connected this back up to the mating end and gave it a shot.  The coach would now downshift when you activated the engine brake switch.  I thought this solved my problem.  My 98 Windsor had the pack brake so I assumed I was good to go.  I was wrong.
  • With the engine brake switch on and low/high switch in low the transmission will select 2nd and start its normal downshifting procedure.  I have checked voltage back at the jake solenoids and I DO NOT get 12v.  I confirmed this with a friend driving while I tested things in the engine bay.
  • If I disconnect the harness from the jake solenoids and jump them with 12V both banks work.  You can hear them and feel them slowing the coach.  So the Jake is functional as a unit.
  • If I put the low/high switch into HIGH but dont activate the engine brake switch on the arm console, the coach will start its down shifting procedure as soon as you let off the gas.
  • My TCL light is on all the time.  I dont know if this would have anything to do with why the engine brake does not work.

My concern is someone was obviously in there messing with this.  Is there a chance they de-activated this in the ECU?  

Looking for some help on where to go from here or what to try.

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