2005 Tahoe "Service 4WD"

[Opus62]

Hi everybody. First time poster here. I recently acquired a 2005 Chev Tahoe LT in fabulous condition. Runs and drives like a dream, purchased from original owner.
There appears to be an odd problem with the 4WD system. Whenever I start it up, the "4hi" light is on. When I try to switch it to "2wd", the "2wd" button light will flash for about 15 seconds then it will go back to the solid "4hi" light. If I push the "Auto 4wd" button, the light will flash for about 10 seconds then it will stay on in "Auto 4wd". When I turn it off then back on, it will go back to the "4hi" light. There are no sounds coming from underneath that resemble any sort of shifting attempt that I can recognize. The truck does not seem to go into 4WD. The "SERVICE 4WD" notice will appear on the DIC but not constantly. I have not yet had a chance to have the codes pulled. Once in a while, when I start up, it will start in 4hi but it will stay there and no other button will do anything. I could press 2wd and Auto 4wd all I want but no lights will turn on or flash, just the 4hi light stays on solid. If I restart, it will go back to the condition I described above. The "service 4wd" notification appears on the DIC but not on a regular basis or in any predictable pattern. I tried to pull the fuse for the 4wd system. When I did, ALL of the lights came on all at once, including the red "N" light.
Sound familiar to anyone?

 

[Sho'Tyme]

Congrats!!! I can't help you but I'm sure someone on here can...Great forum...

 

[Opus62]

Congrats!!! I can't help you but I'm sure someone on here can...Great forum...

Thanx I asked the same question on a Chevrolet forum and, after over 100 views, nobody responded yet.
My problem seems somewhat inconsistent, leading me to believe that it's a bad switch on the dash.

But I could be wrong.

 

[Opus62]

Update:

I am trying to observe a pattern of any sort. Now it seems that if I wait until I see a "service 4wd" message, the buttons are locked in the "4hi" position, which is where they go when I first start up. However, if I push the "auto 4wd" button right away when starting up, the "auto 4wd" light will flash a few times then stay on. If I try to push the "2wd' button at that moment, the "2wd" light will flash for about 15 seconds then go to "4hi". Before now, the "service 4wd" message would appear at random intervals. Now, it appears every time I start the engine. And just yesterday, it DID go into "2wd" mode when I started. This is the only time it went into "2wd" recently. But during my commute, it switched itself to "4hi" while driving. The buttons would not respond until I shut the engine off and restarted.

 

[Opus62]

Update:

I am trying to observe a pattern of any sort. Now it seems that if I wait until I see a "service 4wd" message, the buttons are locked in the "4hi" position, which is where they go when I first start up. However, if I push the "auto 4wd" button right away when starting up, the "auto 4wd" light will flash a few times then stay on. If I try to push the "2wd' button at that moment, the "2wd" light will flash for about 15 seconds then go to "4hi". Before now, the "service 4wd" message would appear at random intervals. Now, it appears every time I start the engine. And just yesterday, it DID go into "2wd" mode when I started. This is the only time it went into "2wd" recently. But during my commute, it switched itself to "4hi" while driving. The buttons would not respond until I shut the engine off and restarted.

Nobody??

 

[donut slayer]

I just saw this thread. Depending on what code is stored, it can be a couple of things. 1, a bad switch, 2, a bad encoder motor located on the transfer case. It also could be the actuator on the front diff but thats rare. C0327 is the encoder motor. The encoder can be rebuilt or replaced for more $$$$$. If it was the encoder, I'd get a new one from rockauto and just be done with it. But thats just me.
BTW, since you mentioned you have the auto 4wd button, you should have the NP246 transfer case. Rockauto has the encoder motor for $164, dorman brand. The switch in the dash is $50, also dorman brand. And if you ever change the transfer case fluid, you'll need the auto trac 2 fluid from GM. Its blue. IIRC it takes 2 qts.

 

[Opus62]

I just saw this thread. Depending on what code is stored, it can be a couple of things. 1, a bad switch, 2, a bad encoder motor located on the transfer case. It also could be the actuator on the front diff but thats rare. C0327 is the encoder motor. The encoder can be rebuilt or replaced for more $$$$$. If it was the encoder, I'd get a new one from rockauto and just be done with it. But thats just me.
BTW, since you mentioned you have the auto 4wd button, you should have the NP246 transfer case. Rockauto has the encoder motor for $164, dorman brand. The switch in the dash is $50, also dorman brand. And if you ever change the transfer case fluid, you'll need the auto trac 2 fluid from GM. Its blue. IIRC it takes 2 qts.

You are quite correct about the transfer case option. NVG246 actually, NP8 on the option sticker in the glove box. I buy from Rockauto quite often. They are much cheaper than local aftermarket, even with shipping to Canada. My research has shown that these systems are rather cheap and easy to work on, making the "shotgun" approach a viable option, something I normally hate to do.

But I am wondering about the front axle actuator. Could it be stuck in the "engaged" mode? I have read a few stories that may support this. One person said that the "pintle" [or whatever it's called] was stuck because of excessive grease or dirty lube...or something. Picture this, I push the 2WD button. the system tries to move the actuator, but it can't, therefore remaining in the 4WD position and setting a code. Until I can get the codes read, this seems to make some sense, according to my little pea brain.

 

[donut slayer]

Getting the code is the first thing. That should tell you what the problem is. Good luck with it.
Didnt know you are in Canada. I went to North Dakota right after Christmas, not far from the Canadian border. High temp was -16*F and the low was -31*F. Never been so cold in all my life. Had a steep learning curve with dealing with the cold. How in the heck can you stand such cold? I'm from Florida and were lucky to see 3 freezing days a year.
My hoe in the snow.

 

[Opus62]

Getting the code is the first thing. That should tell you what the problem is. Good luck with it.
Didnt know you are in Canada. I went to North Dakota right after Christmas, not far from the Canadian border. High temp was -16*F and the low was -31*F. Never been so cold in all my life. Had a steep learning curve with dealing with the cold. How in the heck can you stand such cold? I'm from Florida and were lucky to see 3 freezing days a year.
My hoe in the snow.

You were VERY close to my home town of Winnipeg [home of the JETS!], only about an hour north of ND. I have been to Grand Forks many times. I currently live in Edmonton. We are philosophical about the cold. It's also a point of pride for us. That, and stronger beer!!

I bought my Tahoe from a Chevrolet dealer "as-is" due to its age. The service manager said that he would gladly give me the engine codes but implied that any other codes are useless to us mere mortals.

 

[donut slayer]

Not true about the codes. All you have to do is google them and a wealth of info pops up. Almost all auto parts stores down here will pull the codes for you, free of charge.
Yeah, my nephew is in the Air Force and just got stationed at Grand Forks AFB. We were taking a vehicle up to him. Kinda boring being 19, at a new home not have any vehicle and no friends.