Do Not Shift Light Flashing Allison 748 ATEC

Scott & Heather · March 14, 2018, 01:10:17 PM

We are about 49 miles from our destination of Kansas City and the "Do Not Shift" Light flashes on my touchpad and the alarm sounds. Coach still drives but won't shift gears. No reverse, doesn't downshift or upshift. When I pulled into a truck stop, it would barely move from a complete stop under full throttle. Turned off coach (couldn't even put it in neutral) turn coach ignition back on and the light went out and coach shifted normally for a few minutes of driving before the light and alarm came back and the whole thing repeated itself. The fluid level looks good. I'm not overtemp...retarder is disabled years ago so it's not that....any thoughts?

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eagle19952 · March 14, 2018, 01:26:13 PM

fluid ?

Scott & Heather · March 14, 2018, 02:28:47 PM

Fluid seems to be at a good level on dipstick. But I could add some. Problem is I have transynd in there and no transynd at the truck stop. What can I mix it with? 15w30? Dextron?

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Templar52 · March 14, 2018, 02:46:29 PM

Sir,whent you start your engine,if ever you depress the fuel at the same time,this will happened.
Check if you have dirt under your fuel pedal . If yes,the pedal is not comming back at it normal idle position.
Clean every Little Rock that can go there.

luvrbus · March 14, 2018, 03:07:46 PM

It is in the limp mode Scott probably a bad ground on the DDEC engine,if you have reset the transmission

Scott & Heather · March 14, 2018, 03:51:09 PM

Yep. Limp mode. Every time I turn the coach off and then back on it resets and it works fine for a little while and then it does it again. I've added transmission fluid it's still behaving the same way. So where do I start looking for a bad ground related to something like this?

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HB of CJ · March 14, 2018, 04:21:44 PM

Do you have a dedicated grounding strap from the transmission to the frame? Are your battery cable connections clean and good? Any physical dirt in the works within the shifter button console touch pads?

Or ... like already said, physical crud somewhere in the foot throttle? Are the physical connections clean and dry. Any other poor continuity or grounding symptoms anywhere else in the Bus Conversion?

Scott & Heather · March 14, 2018, 06:07:43 PM

Ok I'll check
All
This. But another data point:

When it just happened, I didn't restart the bus this time to reset it. I just unplugged the touchpad only while the coach was running. This fixed it probably temporarily. Does this point to a touchpad issue?

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luvrbus · March 14, 2018, 07:11:18 PM

Check the connections on the speed sensor

Bill Gerrie · March 14, 2018, 07:12:05 PM

Are any codes present? Shut engine off. Place trans test switch "ON". Start engine. Shift from "N" to "R" and back to "N". If codes are there this will clear them. What ever you do don't rev it up and it doesn't move. You will fry a clutch pack faster then you know.

Scott & Heather · March 14, 2018, 07:26:48 PM

Cliff, my speedometer isn't working either all of the sudden...another clue?

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solardude · March 14, 2018, 07:42:06 PM

You don't need to have the engine running to reset the codes, just have the key in the "on" position.

I also have an intermittent "ground" somewhere. Mine throws a "low reverse pressure switch" code sometimes. I was told this is common problem with the harness between the computer and the valve body. the guy I spoke to is an "old salty" heavy equipment Allison guy.

I have not had the time to fix mine yet, as I am not ready to dig into the valvebody and wiring.

I hope this turns out to be something easy for you, I have heard the grounding problem can be a real challenge on the ATEC.

SolarDude

solardude · March 14, 2018, 07:51:08 PM

I vaguely remember someone on this forum saying the speedo has a hall effect sensor somewhere on the front tires.

I know that is not helpful, I'm sure one of the experts will chime in shortly.

SolarDude

Geoff · March 14, 2018, 07:56:34 PM

Aren't computers nice? You have to go through every harness connection, take it apart, clean the terminals, slightly crimp the female ends, put it back together and hope for the best.

Scott & Heather · March 15, 2018, 02:36:06 AM

Thanks Solar...I'm flying out of town for a couple weeks so I'll have to chase this down later unfortunately. Geoff, I am absolutely convinced after a mere three years of ownership that I would rather have my mechanical 6v92 and Allison HT740 back any day...seriously.

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