Shift Indicator Malfunction / No 4 Low

kper · January 31, 2015

I am new to the forum and I'm hoping somebody can help me out with an issue but first some history. My son is serving out of state and through me he purchased a 2000 Silverado with 89k miles for delivery to him at a later date. I did an extensive test drive before the purchase which included testing all the 4x4 functions which operated as designed. Before I delivered him the truck I had a few things done, one of which was having tranny flushed and fluid changed in the t-case by a very knowledgable tranny shop that I've used for over 20 years. While they had it they replaced the problematic rear main seal and housing on the engine. They are good friends and I trust them immensely.

Fast forward a week and I find myself delivering the truck to my son and while I'm explaining the 4x4 functions we discover 4 low isn't working. 4 high seems to work - indicator light illuminates and the front axles seem to be engaged. Auto 4 light illuminates but we didn't have a good surface to test it on. 4 low flashes until it times out and returns to 2 high. We tried the 1-3 mph roll in neutral, stopped, backing up.... nothing worked. Then we noticed that when the truck was placed into neutral the shift indicator would indicate neutral then in the blink of an eye, and as fast as it lit up, the indicator rolled from neutral to reverse to park and then none were lit up - literally all within a blink of an eye. - all while the trans was in neutral.

I am not home so I do not have access to a code reader but I'm sure I could go somewhere and have it done.

Has anyone heard of this before? Any thoughts?

Thank you.

gmtech4 · January 31, 2015

,NSBU switches are junk on these trucks ,

Yours seem to be a little sluggish ,

If the connector does not want to come apart , us a small smal torch and warm the switch , this works VERY well ( sealant becomes like a glue with time )

Scanning the TCCM will not get pulled by a POS code reader

kper · January 31, 2015

Sounds like a neut safety sw? Could this have been something caused with tranny shop removing the trans? I'm guessing they'd have to remove connectors - I don't know how many there are.

gmtech4 · February 7, 2015

Sounds like a neut safety sw? Could this have been something caused with tranny shop removing the trans? I'm guessing they'd have to remove connectors - I don't know how many there are.

Sorry for not seeing this til now to answer ,

The NSBU, (neutral start back up) o

Lives on the shifter shaft , the connectors can be a pain as I said , a tranny guy does not need to remove it to rebuild the tranny ,

They get moisture in the switch and they pooooop the bed , they are tight going on the shaft , I alwayssand the shoulder where the nut butts up against to help the switch slid on , if you can do it , go ahead , , there is an adjustment as you can see where the mount bolts live

kper · February 7, 2015

I can still start the engine in neutral - that doesn't sound like a defective switch, does it? Or are talking two separate circuits?

kper · February 8, 2015

New development...

My son called and said the selector is now reading inaccurately. Park when in reverse, reverse when in neutral, neutral when in drive and so on. I'm wondering if the switch simply is out of adjustment, if that's possible.

gmtech4 · February 8, 2015

New development...

My son called and said the selector is now reading inaccurately. Park when in reverse, reverse when in neutral, neutral when in drive and so on. I'm wondering if the switch simply is out of adjustment, if that's possible.

Check the shifter cable at the bracket at the tranny , the tabs can break and the "fence staple" retainer maybe gone causing an loose cable /gear indicator

kper · February 8, 2015

Thanks for the advice. It'll be about 3 weeks before I see the truck again but that gives me some optimism that we can track down this problem.

gmtech4 · February 10, 2015

Thanks for the advice. It'll be about 3 weeks before I see the truck again but that gives me some optimism that we can track down this problem.

If the cable is done a replacement is required and the adjustment is rather different and service info is required when replacing the cable IF ITS A 2 PC CABLE ( lower half only required )