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Topic: Transmission Gremlins  (Read 1492 times) previous topic - next topic

Transmission Gremlins

Hey Foretravel Gurus,

This one is a bit long, but just trying to cover everything the first round.

I am having a few Gremlins showing themselves in the Allison.

The rig:  1990 GV U300    DD6V92    Allison MT 600 or 700 series , not sure which, (with a  push button control pad)

Quick description,

I took the rig out of storage and headed for fuel.  The rig was running perfect until I began to slow down to enter the turn lane into the fuel station.  I started hearing beeping coming from the transmission gear selector pad and noticed the Check Trans light came on and the DNS..."Do Not Shift" light was flashing.  I pulled into the fuel bay, at slow speed, and set the park brake and shut the engine off.  I cycled the key a couple of times and the DNS light was still flashing.

I then did the following:

-Checked the transmission temp.  It was nice and cool.

-Checked the battery voltage on the dash. It was reading around the 13V mark.

-I fired the rig back up and checked the fluid level and it was indeed quite low, very near the end of the dipstick.  I added two quarts.  I then shut it down and cycled the key, no change with the DNS light. Still flashing.

- I toggled the Transmission Code Reader to the on position and received a "22" code (Speed Sensor Fault)

-I crawled under the rig and checked all of the wiring looms to the electrical connections.  I moved the looms around to see if there was a short anywhere.  I then unplugged the main electrical connector (large round  pin connector) and checked the connection and condition of the pins.  Everything was very clean and dry inside.  I proceeded to follow the small loom toward the rear of the transmission and arrived at the speed sensor two wire connector.  I unplugged it and found it was also in good condition.  I did not remove the actual Speed Sensor.  I cycled the Ignition key a couple of times and still no change with the DNS light...Still Flashing.

- Talked to Keith Risch and he suggested pulling the connectors at the computer and checking the condition of the pins.  The connectors are held in place by a small bolt from the bottom.  I did not have my toolbox so I jumped in the TOAD and ran to the house.

-I was gone maybe twenty minutes and got a call from my wife.  She said she turned the key, just to check, and the DNS light had stopped flashing.  Huh?  Well I made it back to the rig, turned the key, and sure enough the DNS light was indeed off and the rig fired up and went into gear as if nothing had ever happened. 

- I checked the diagnostic code reader with the toggle switch and it was no linger flashing ANY type of codes at all.

- I drove the rig home and it ran perfectly and believe it or not, the transmission fluid was spot on the full mark, so I got lucky with the amount I added.

Soooo... what do you guys think?

-Does low fluid trigger a DNS light and limp mode?  If so, does the system just reset itself after being topped off, after a brief delay?
-Does this sound like a Speed Sensor going bad? 

-Just trying to figure out why in the world the DNS warning light would suddenly fix itself while I was away from the rig for half an hour.... 

Any ideas?

Thanks y'all

Jeff

Re: Transmission Gremlins

Reply #1 –
Just a wild guess but maybe it takes a minute or 2 for the transmission fluid to get where the low fluid sensor is. I'd be more worried about why it was low.

Re: Transmission Gremlins

Reply #2 –
Jeff,
For reference you might check out the issue I had with the oil pressure switch which was stuck "on".  The switch lets the transmission know the engine is running.  Your symptoms seem to indicate that the transmission thinks the engine is off; even though it isn't.
Yours's could be stuck off or the wiring on it is corroded and intermittent. 
See Reply 5 in here: 1991 Grand Villa Check Trans Light is on
But reading that whole thread might be useful.

Also for reference are a few schematics that I scanned from my manual.  I have a 1991, but I'm pretty sure our power trains are identical.

Re: Transmission Gremlins

Reply #3 –
Wow John, that's great you have those wiring diagrams. I'd love to see diagrams for our 92 U240. They would be helpful.

Jeff, I hope your problem never resurfaces but I'm glad it worked out without event.

Michael

Re: Transmission Gremlins

Reply #4 –
Quote from: JohnFitz –
Jeff,
For reference you might check out the issue I had with the oil pressure switch which was stuck "on".  The switch lets the transmission know the engine is running.  Your symptoms seem to indicate that the transmission thinks the engine is off; even though it isn't.
Yours's could be stuck off or the wiring on it is corroded and intermittent. 
See Reply 5 in here: 1991 Grand Villa Check Trans Light is on
But reading that whole thread might be useful.

Also for reference are a few schematics that I scanned from my manual.  I have a 1991, but I'm pretty sure our power trains are identical.

Thanks John,
I will keep an eye on that oil pressure gauge.  You never know.
Jeff
 

Re: Transmission Gremlins

Reply #5 –
Quote from: Michael Riensche –
Wow John, that's great you have those wiring diagrams. I'd love to see diagrams for our 92 U240. They would be helpful.

Jeff, I hope your problem never resurfaces but I'm glad it worked out without event.

Michael


Michael,
I sure hope that Gremlin fell off going down the highway, never to return... Fingers crossed.
Thanks for the well wishes.
Jeff