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Old 06-15-2020, 08:30 PM   #1
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Downshifting Early

We went on a short trip a couple of days ago to dump tanks and coach was fine. On the way home the first time I went to slow down for a stop, I took my foot off the throttle and the trans immediately downshifted enough to send the RPMs over 2500. The check engine light came on and I pulled over. As soon as I stopped the light went off. After checking for leaks and overheating we started up again. Next stop, same thing. Every time I take my foot off throttle, downshift more than usual and check engine light comes on. Goes off when I stop. The wife admits she may have pushed the downshift arrow by mistake while repositioning the coach at the RV dump but we shut off the engine for a bit. I am at a loss. Any help is appreciated.



Phil



2008 Tiffin Phaeton 42 QRH

Allison 3000 MH 6 speed
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Old 06-15-2020, 08:47 PM   #2
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This procedure may help with receiving any codes the system may have


https://cdn.mpparts.com/pdfs/Trans%20Codes.pdf
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Old 06-16-2020, 06:02 AM   #3
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Very helpful! Thank you sir!
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Old 06-16-2020, 04:59 PM   #4
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Sounds like you have an exhaust brake and it is doing what it is supposed to - set a target gear (look at the shift panel - usually 2nd or 4th gear) and start down shifting to help you brake, when you take your foot off the accelerator pedal. If you press the accelerator pedal, does it go back to showing 6th gear and act normal?
You should have a switch on the dash, maybe marked Exhaust Brake? Turn it off and see if that cures what you're seeing.
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Old 06-17-2020, 05:56 AM   #5
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I would agree with you that it sounds like the exhaust brake is working, it just hasn't set off the check engine alert before. i didn't try to accelerate because it caught me off guard but I will try that and see. On my coach, it's a two stage compression(low/high). Had it set on low.


The link 1doodad sent had good results. No tranny codes but the fuel level code I got is "TL oL". That one is not on the sheet. Still trying to figure it out.


Thanks. This is making more sense.
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Old 06-17-2020, 09:45 AM   #6
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Oops. I meant trans oil level not fuel level. Was only on first cup of coffee.
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Old 06-18-2020, 10:41 AM   #7
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Quote:
Originally Posted by Bigtoado View Post
I would agree with you that it sounds like the exhaust brake is working, it just hasn't set off the check engine alert before. i didn't try to accelerate because it caught me off guard but I will try that and see. On my coach, it's a two stage compression(low/high). Had it set on low.


The link 1doodad sent had good results. No tranny codes but the fuel level code I got is "TL oL". That one is not on the sheet. Still trying to figure it out.


Thanks. This is making more sense.
Ok, I'm out of my knowledge realm if it is not an exhaust brake.
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