# truck threw out a code



## RBRONKEMA GHTFD (Dec 17, 2006)

Hey guys, I was driving home friday from work and notcied my check engine light was on, on my 04 sierra. I stopped at one of the local autozones and they went to read the code and it wouldn't read cause apparently I had a fuse that was blown. I went home, found the blown fuse (cig lighter, which I don't use, nor do I know why or how it got blown). I went back the next day and they were able to read the code to me and I got a PO700 and a PO708. The 700 apparently is a transaxle control system fault. Basically the module has a fault in it?. And the 708 is defined as Transaxle swtich circuit high. basically stating that the ecm has detected all input circuits high with non pulled low. My question is has anyone ever had these code get throw out at them and what am I looking at as far as cost to get this fixed and could I do it myself? The only thing I can think of that would of throw these code out at me is when I pulled one of our mowing trailers on friday with a broken mower on it. The mower was over the axles but we couldn't get it to come any futher on the trailer so I am thinking that that might of had something to do with it. Whats the next step?


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## nicksplowing (Oct 5, 2005)

i will check at the shop tommorrow on the computer for ya what exactly could set that code


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## William B. (Jul 22, 2004)

Here is some stuff I found while searching on DP. Are you running a chip on your truck? If you are you might want to turn it down.

http://www.dieselplace.com/forum/showthread.php?t=237102&highlight=PO700
http://www.dieselplace.com/forum/showthread.php?t=177306&highlight=PO700

http://www.dieselplace.com/forum/showpost.php?p=2461868&postcount=11
http://www.dieselplace.com/forum/showthread.php?t=72558&highlight=po708
http://www.dieselplace.com/forum/showthread.php?t=142119&highlight=po708


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## B&B (Nov 4, 2006)

The P700 is simply a MIL request code that the transmission controller (TCM) sends to the engine ECM in order to illuminate the check engine light...standard issue procedure anytime you have an issue with an Allison. Basically just maes the engine ECM aware that there's an issue with the trans or its related components.

The P0708 is the lead to the actual issue. Which is as you described, a high voltage issue...but it has specifically to do with the NSBU switch on the trans. And I'm sure if you do much reading on the web you already know that the NSBU is a common problem on these trucks. They're not sealed as well as they should be where the two halves of the switch are assembled which leads to moisture...which like in any electrical device then leads to corrosion.

Change the NSBU switch and double check the wiring harness running down to it for any chafing/ rub through issues (also somewhat common on the D-max equipped trucks in these years). The blown fuse isn't like to be related to this issue. Was probably blown previously...you just didn't discover it until you went to pull the codes out (cig lighter and OBD2 diagnostic port use the same fuse for power supply).

Did the trans operate normally after you got the CE light? Should have been in limp mode by then.


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## RBRONKEMA GHTFD (Dec 17, 2006)

B&B;563218 said:


> Did the trans operate normally after you got the CE light? Should have been in limp mode by then.


The truck runs and drives just fine. I have heard about the NSBU switch many of times on here alone. Where might one find that NSBU, and how difficult is is to change out? I am pretty mechanically inclinded, but I just don't want to F something up to where it will cost more than what I want it to. Basically if I bring is somewhere and they F it up they have to pay for it ya know. Alos how much might a NSBU be?



William B.;563217 said:


> Here is some stuff I found while searching on DP. Are you running a chip on your truck? If you are you might want to turn it down.


The truck is as stock as can be except for the 285 75 16 BFGS I am running. I would like to chip it but then with the luck I have it will break and I don't need nor do I want that.

I should also add to this that when the truck is in drive the indicator light isn't on. And it hasn't been for sometime. It will come on everynow and then but then it will shut off. Is this something related to the problem at hand? It started doing this, this past winter. I just figured it was because my gauge cluster is F'd up. I did get a recal on that but it was only for gauges sticking.


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## B&B (Nov 4, 2006)

RBRONKEMA GHTFD;563380 said:


> I should also add to this that when the truck is in drive the indicator light isn't on. And it hasn't been for sometime. It will come on everynow and then but then it will shut off. Is this something related to the problem at hand? It started doing this, this past winter.


That right there is the #1 classic symptom of a failing/failed NSBU switch.

They're pretty easy to change and if you do a search here in the Chevy forum there was a thread a few months back about this issue and the procedure for changing the switch...even includes pics. The toughest part is getting the connector plugs disconnected from the switch. GM used a sealant in the connector to prevent corrosion (should have paid more attention to the switch itself). A heat gun works well to soften the sealer...they'll usually slide right out then. Be gentle with the heat gun though..

Don't go to GM for the switch, go to an Allison dealer as their half the cost there. Should be around $60-$100. They cost $200 from GM in many cases.

Make sure you clear the codes after changing the switch.


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## William B. (Jul 22, 2004)

Check out Merchant Automotive over in Holland. He carries them.

http://www.merchant-automotive.com/


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## RBRONKEMA GHTFD (Dec 17, 2006)

B&B;563398 said:


> That right there is the #1 classic symptom of a failing/failed NSBU switch.
> 
> They're pretty easy to change and if you do a search here in the Chevy forum there was a thread a few months back about this issue and the procedure for changing the switch...even includes pics. The toughest part is getting the connector plugs disconnected from the switch. GM used a sealant in the connector to prevent corrosion (should have paid more attention to the switch itself). A heat gun works well to soften the sealer...they'll usually slide right out then. Be gentle with the heat gun though..
> 
> ...


I kind of thought so but I wasn't sure what was going on there. I'll have to stop by the place that Will B. said and he'll be able to hook me up. Plus he is right around the cornor from my house too.



William B.;563454 said:


> Check out Merchant Automotive over in Holland. He carries them.
> 
> http://www.merchant-automotive.com/


Thanks Will. I would of never thought about that place until you said something. I just looked the part up and its 70 Bucks. Thats cheaper than what I thought, plus he should be able to clear the code for me too.


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## William B. (Jul 22, 2004)

Check out dieselplace.com I'm pretty sure there is a DIY step by step thread on there showing how to switch out the NSBU switch as well.


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## RBRONKEMA GHTFD (Dec 17, 2006)

William B.;563779 said:


> Check out dieselplace.com I'm pretty sure there is a DIY step by step thread on there showing how to switch out the NSBU switch as well.


Thanks again To all who helped out. I am hopefully if I get time, going to take care of this on friday but we'll have to see what happens with work and what not.


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## RBRONKEMA GHTFD (Dec 17, 2006)

So get this, I am driving to work this morning and I notice that my check engine light is off and my indicator light for my gear selection is back on. WTF?!


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## B&B (Nov 4, 2006)

RBRONKEMA GHTFD;564184 said:


> So get this, I am driving to work this morning and I notice that my check engine light is off and my indicator light for my gear selection is back on. WTF?!


Totally normal when dealing with a failing NSBU switch as well. Surprised it's never gone into limp mode yet though.


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## RBRONKEMA GHTFD (Dec 17, 2006)

B&B;564193 said:


> Totally normal when dealing with a failing NSBU switch as well. Surprised it's never gone into limp mode yet though.


Lets just say I am very glad it hasn't gone into limp mode yet. I am going to go to Merchant tomorrow and get that new swtich.


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