# Duramax Question



## yamahartx (Dec 24, 2009)

I have an '05, second year plowing with it. First year commercially. 

My question is when in down pressure mode on my plow and back dragging, I have had it twice make a pretty good clunk jumping into a safe mode. Then it shuts down reverse and drive. Then I have to shut the truck off and let it reset it self. 

Has anyone else have this problem and if so, can you direct me to the sensor that might be going bad before it stops me completely.

Thanks, Brent


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## William B. (Jul 22, 2004)

Sounds like you are limping the transmission for some reason. Usually once the tranny has limped, it becomes easier and easier for it to do it again. What is happening is the computer noticing to much slippage between clutches and then goes to limp mode. Eventually the tranny will need to be rebuilt.

Have you done any service to the tranny, ie filters changed(there are 2,internal and an external) fluid checked/changed etc?


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## lilweeds (Aug 3, 2007)

Good chance the PRNDL switch needs to be replaced. Check diesel place.


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## Ctll (Jan 2, 2008)

Could need to adjust or replace the the shift cable,truck could be flexing just enough to pull it slightly out of the selected gear and the computer thinks there is something bad wrong so it shuts down. I had some problems with mine and thought it was the neutral switch too, shift range inhibited it would say on the dic and not going into the same gear as it was showing on dash or would not show on dash at all. Ended up being the shift cable had broken the center wire at the middle conection and only the frayed wires were moving th gear selector at the tranny. Easy to check at least, and you can make sure it is adjusted right while you check it. I drive it all the time so I had not notice how sloppy shifter was until I fixed it.


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## tuney443 (Jun 25, 2006)

Put it on a GOOD scanner to diagnose it.Stop the guessing.


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## stacks04 (Jan 22, 2008)

Bring it to get the codes read, repost here and better thoughts to follow. Anything trans related will set a code, you need a good code reader that will read the allison tcm though, not just the ecm. Odds are its the neutral safety switch, but not worth guessing.


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## rcpd34 (Jan 16, 2004)

Sounds like PRNDL switch. Had that happen on my '04.


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## yamahartx (Dec 24, 2009)

I just recently changed all fluids, filters including transmission. It gets regular maintenance with synthetic since I have owned it at 20,000 miles.

After I posted this, I hard wired in an amber light and went to remove the cables from one of my batteries and realized it was finger tight. Along with the truck being in a heated garage for awhile and was able to melt down all the ice and snow from under it. I just recently plowed 10" of snow for 9 hrs without issues. Not sure if the loose wire would cause such an issue, or so much ice built up may have pulled on something, but if or when it happens again it will go straight to the shop for testing.

Getting a little crunching in the left front....it will be heading to the shop anyway soon.


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## 496 BB (Feb 11, 2010)

A losse battery cable WILL cause that. Ive had frayed ones do the same to my Allison. She can be moody somedays, be happy somedays, and I swear the other days she rode the short bus from the factory


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## JustinD (Jan 14, 2008)

Switching from drive to reverse too fast will do it too, they don't like to change direction unless its stopped completely


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## woodchuck2 (Dec 4, 2010)

As some of the others mentioned it is most likely the switch on the tranny, with you back dragging the snow it is probably piling up under the truck and you are getting water intrusion in the switch and you could be flexing the shift cable as mentioned too. These trucks were noted for these switches until 06. 2006 and newer has the switch inside the tranny.


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## yamahartx (Dec 24, 2009)

Thanks everyone, so far so good.

My plan is not to be so lazy and remove the plow in the shed every night and get the truck in the heated garage to melt down after plowing.

Thanks again! Brent


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## poolboy (Sep 30, 2009)

If it is the "neutral safety backup switch" on the tranny, buy an AC delco part. I have had too many issues with the other brand ones in friends trucks. Igot ine from napa and it came in an ac delco bag.


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