Probably the NSBU switch-- it is located on the drivers side of the trans.

 

What's the acryonmn for NSBU? Netural safety backup?
Can I disconnect it to test if it's working?
Gary

 

i had the same problem but my xcheck engine light comes on when it does it and i go through my banks system and clear the code and it is fine maybe you should get it put on a code reader to see if it something like that

 

Lots of problems with the switch on the 5 speeds-- it gets water inside and shorts. The new switches are sealed better. Just replace the switch!

 

when did the switches get better? typically how long does the original last?

 

Thanks guys, I picked up with switch at Napa. Made in Taiwan, but people have had success with theirs and I only paid $40. If this doesn't work, I'm getting a new ignition switch which seem to have fixed the issues with those who had similiar issues.

I'll post pics of the switch tonight.

 

The napa switch has a slight gap on one side that should be sealed. I'm going to seal it with silicone sealant.
Gary

 

I got home tonight with the new Napa NSBU switch, but for kicks, I started the truck to see if it would go into reverse even thought I wasn't going to work on the truck tonight. I had a feeling if it was the NSBU switch that all the rain we've had somehow caused moisture to get into the switch even though I haven't driven the truck in about two weeks (if the truck hasn't moved, how do you get moisure in the switch since I'm not splashing water all over the underside?!). I had a feeling it (the nsbu switch) dried out so it should go into reverse. So after the truck was started and warmed up for about a 30 secs, I move the gear lever to R. Hmm.. it wasn't blinking the letter "R" (for reverse) like this morning. I then released the brakes and was able to reverse!!

The problem solved itself! I should still keep the NAPA switch as I know it's going to go bad again. I'm not sure how moisure would get into the NSBU switch because the truck hasn't moved and there is no water from above. Must be from the frost in the mornings.

What would you do in my situation? Return the NAPA NSBU switch or keep it?

 

id say change it given its history of failure....

 

For 40 bucks I would change it and throw your other one in the trash...

 

I'm gonna keep it, thanks guys. Can't go wrong for $40+tax. I'm going to try to seal the switch when it gets warm....
Gary

 

same issue

i have the same problem. i have replaced the reverse neutral switch . basicly i did a PPE stage 5 rebuild i hooked up a bullie dog power pup tuner with a crazy larry tune and did an on the fly program change. i parked the truck and when i started it back up it just flashes R.

it coded p0700 which is a general transmission error code so i had the TCM read and it is showing now error codes.

what could the issue be? i heard it could be a fried ECM any truth to this.

thanks
jon
'02 2500 hd, PPE Stage 5 tranny 5in dual stacks

 

With the Allison transmissions, when they are cold (cold outside) they will go into a safety / protection mode until the fluid warms up, this protects the transmission. The Transmission Control Module (TCM) - computer (with a reading from the temperature switch in the transmission pan) puts the transmission into a “limp” mode in case you have to move the vehicle. I believe it is second (2nd) gear. I don’t think the Service Engine Soon (SES) light comes on for just normal warm up, but the “D” will blink. So, in cold weather a warm up is necessary. My issue was too severe and the SES did come on – read on.

My issue started right after I changed my transmission fluid and it just happened to be at the start of winter. A short time later, about a week, on a cold morning the truck wouldn’t move, and the reverse “R” would blink and the Service Engine Soon (SES) light was on. After a LONG warm up, and cycling the start / drive procedure, all seemed to be normal. When the temperature outside is warm, or truck / transmission is warm, all is fine. Only when the temperature drops and a cold startup is when I have the issue. The colder the temperature outside the worse the issue and the longer it takes to move the truck (pretty obvious).
After I start and stop the vehicle enough (cycle the start / drive procedure) the SES goes off, codes stay in history though. Code 700 just told me there is a transmission problem – to scan for the transmission codes from the TMC for further diagnosis. I forget what the other code was.

I believe it is the transmission temperature switch / sensor, which is also the shift pressure solenoid / switches for all gears; it’s all one unit, flat, fits in the palm of your hand. My synopsis is that when I changed the transmission fluid, it “cleaned out” the switch and caused the switch to malfunction and causes the issue. I am going to change the temperature switch (inside the transmission pan, attached to the valve body – fluid flows through the switch) and I bet it fixes the problem. I will also change the inner filter while I have the pan off; the truck only has 141k miles. Right now (February) I use a magnetic pan heater, plug it in and warm up the fluid a couple hours before I leave. Cold mornings it works great, this morning, 15 degrees out, not so good – LONG warm up.

I have noticed that if I do not cycle the start / drive procedure, the truck will not move even with the rise in transmission temperature (shown on the gauge).
Cycling = (after warm up, transmission temp gauge has risen) put truck in gear / park, shut off, remove key, open door. Have to repeat this (start / drive cycle) 3 – 5 times before the truck will move. I guess it kinda–like resets the TCM.

Sorry this is so long but a lot of the explanations here are very vague and leaves yah wondering sometimes, just trying to be accurate.

I will reply again when I replace the switch and let you know if that was for sure the issue. I just replaced the fluid so I am hesitant (cheap) to drop the pan again so soon.

V/r TOP

2007 GMC, 2500 HD

 

This is what the switch looks like.

V/r TOP

 

Yup, I replaced the shift pressure solenoid / manifold pressure switch / oil pressure solenoid (depending on who you buy it from as to what they call it) which is also the temperature sensor, and it fixed the problem and is spelled out in the situation I wrote about above.

One note though; don't buy this part from NAPA. I did and it was faulty, had to drain and drop pan again. Bought another from GM and then it was fixed.
Hope this helped.

 

I started my truck up this morning, 2002 silverado cc lb, warmed it up, put it in reverse, but it would not get into gear. I noticed that when in "R" it was blinking. I was able to put it in D 3 and 2 and I can feel the tranny go into the gears but I couldn't move much because my other car was in front of it. I decided to shut down and take my other car to work. Anyone know what's going on? Is my tranny on the way out? I just bought this truck with over 200k miles on it and it's been running great for 2 months. I haven't driven it in about two weeks and it's been cold and rainy (not sure if that has anything to do with what's going on). Gary

So I'm not a mechanic but I love chevys- I had an 02 gmc 8.1 liter atomatic Allison and I had the same issue: if you shut the truck off wait 3 - 5 seconds it should go into reverse this is a potential temporary fix as I discovered it to be a "Reverse Nuetral Switch" I've got a great mechanic who replaced it and it cost about $200 including labor. Sadly that truck was ttotaled and my replacement is an 02 Chevrolet Silverado 8.1 w/ Allison transmission and I had this happen on Thursday but due to trashed transfercase that I just sunk $3100.00 into I'm to broke so I'm looking into fixing it myself?? But not sure if I can, lol P.s. don't ever park where your blocked or pnned in, that's when crap happens lol good luck!!!