Does this sound like a NSBU problem

I'm having problems starting my 2500hd GMC/duramax w/ allison when its warm and I turn it off for a few minutes it won't restart. The engine cranks but will not start. My dealer can't figure it out. A different dealer told me that it was from fuel thining out when turned off (15 min) and was losing pressure in the fuel system and then did not have enought pressure to start. My normal dealer says he sees a code for the NSBU and that is what the problem is. I have had no transmission issues. loss of gear indicator, and no codes in the message box.

Would the NSBU control the fuel flow to inhibit starting?

Beside they told me it was about $500.00 to replace which does'nt sound right to me.

I have searched under NSBU but have found no similar problems.


Thanks

Philip

I don't have a lot of technical info, so I am sure others will help you out regarding the possible fuel issue.

If your NSBU switch is the problem....I can tell you when my NSBU went south it caused the gear indicator to flash. I bought mine from an Allison dealer for about $50 (IIRC). Aside from having a difficult time getting one electrical connection to come apart, replacement was no big deal laying on the garage floor. I bet it didn't take over 45 minutes, going slow and following the directions from this web site. If you do a search you can probably still find them. So $500, way out of line.

Dawg

I just had a NSBU go out while driving a 2001 2500 HD CC 4X4 which I've had very few problems with since new. Mine took a dump while driving which in turn took out the starter relay / fuse under the hood causing me no choice but to get a tow to the dealer. I lost the tranny indicators when it puked out on me and I had an idea it had something to do with the NSBU. Why it took out the starter relay couldn't be explained so I sat dead on the side!!
All said and done it started out at $400, but then they found a flat spot on the starter caused by what?? They don't know!! It ended up $782 plus $100 for the tow. The starter definitely works much better than the original so I can't complain too much on a 7 year old vehicle with 70K miles. Starters this old are eventually going to go. If I were you I'd replace that switch myself because they are only around $50 from an Allison dealer and it's not very hard to do. The newer trucks from I believe 2007 on have the NSBU inside, but the dealer told me they've still seen a couple go out. This will rule that out as the issue on yours and I don't think it's that anyway. These early model Duramax trucks have some "ghost" issues that seem to pop up from time to time and I've heard that from others as well.

Good Luck!!

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Originally Posted by konacat

I'm having problems starting my 2500hd GMC/duramax w/ allison when its warm and I turn it off for a few minutes it won't restart. The engine cranks but will not start. My dealer can't figure it out. A different dealer told me that it was from fuel thining out when turned off (15 min) and was losing pressure in the fuel system and then did not have enought pressure to start. My normal dealer says he sees a code for the NSBU and that is what the problem is. I have had no transmission issues. loss of gear indicator, and no codes in the message box.

Would the NSBU control the fuel flow to inhibit starting?

Beside they told me it was about $500.00 to replace which does'nt sound right to me.

I have searched under NSBU but have found no similar problems.


Thanks

Philip

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I doubt it's the NSBU, but I do think it's related to fuel-rail pressure - like what was suggested. The commanded & actual pressures can be seen with a Tech II scan tool. A problem with injectors that produce a high fuel return rate can cause this, as could a worn Bosch hi-pressure pump, or fuel pressure regulator or fuel pressure sensor... I'd change the fuel filter as a first step. :)

Jim

I have a 2003 Duramax with 6 speed manual transmission and have the same problem with starting when warm. My truck has ~50K miles and just started this about a month ago. Only thing I've tried was to re-prime after about 30 minutes from warm shutdown, didn't make any difference. Cold starts from ambient are normal. I'm going to get it in to the dealer next week, will post what I find out.

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Originally Posted by fixitup

I have a 2003 Duramax with 6 speed manual transmission and have the same problem with starting when warm. My truck has ~50K miles and just started this about a month ago. Only thing I've tried was to re-prime after about 30 minutes from warm shutdown, didn't make any difference. Cold starts from ambient are normal. I'm going to get it in to the dealer next week, will post what I find out.

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Finally went to the dealer to have checked out, they confirmed it was bad injectors and replaced under warranty.