I have a completely stock 2005 Silverado 4dr 4x4 that I use as a daily driver. Recently it just decides to engage the 4wheel drive whenever it feels like it. When it does this I cannot just push the 2wd high button, it will blink for a few seconds but then stay in 4wd high. I have to push the Auto 4wd button and then the 2wd high and everything is ok.

This has happened every 3-4 days while driving, usually when pulling away from a dead stop.

Is it the switch or could it be a bad ground or something like that??? Any help or ideas are appreciated. I tried searching but could not find anything.

 

My truck has been also engaging in 4wd randomly, but then I can go right back to 2wd. This problem started two weeks ago when I noticed the front wheels were not engaging. Gremlins...

 

I would think its encoder related or switch related. I would check the connections on your T-Case encoder first...pop the connector off, and clean the pins with contact cleaner both on the wires and the t-case side. May as well do it to the front diff encoder too while your under there.

 

I have had this problem on my truck as well, if your truck has the in dash 4X4 switch like mine pull the switch out and check the pins that go into the back of the connector, I have seen a few where GM crimped them come loose over time. The best fix is to pull it apart and solder the pins together. Hope this helps.

 

You need a new encoder motor. They must have had a bad bunch in the batch in 2005 because I've seen about a dozen of these do this and they were all 2005s.

 

I'm on my 2nd encoder motor solenoid (ring) in 100,000 miles. It and a new gasket are a fix. The 4WD gets screwy...on off....or no lights...intermittent progressively getting more common. Problem is the ring is not working and the vehicle no longer knows if the 4WD is engaged or what. Notorious problem for 05 and 06 Avalanches (and other GM 4WDs I hear). The switch problem was common in older models (i.e. my dearly departed 2000 suburban). I think you should be able to match the signal at the switch with the signal at the encoder motor to pinpoint where the problem starts.

 

That is the fix for the C0327 and service 4wd light but it is not the cause for the transfer case shifting on its own or neutraling out. The NP246 transfer case uses a clutch pack to put power to the front shaft. The encoder motor moves a fork that squeezes on the clutch pack and there is an electromagnetic brake within the encoder motor that holds the encoder motor in place once the clutches are applied, released, and range is selected. Its the magnetic brake that fails and causes them to float around between ranges. This is also the reason why the cheaper 3/4 ton and 1 ton encoder motor will not work, they have no magnetic brake.

 

My examples due to switch and encoder ring were at startup (not in transit like OP) finding it in neutral, 4WD Hi, 4WD Lo, or sometimes still in 2WD but no lites. More to the real point I recommended the OP do a little voltage reference match-making between switch and encoder first to narrown down what he was replacing (or something as cheap as a wire/connector). But changing the parts one by one seems to be popular too. cheers

 

That is fine too but based on what he said it still needs an encoder motor.

 

More than likely its the encoder motor.. I did mine a few months back and its easy to do.. I even took some pics.

my truck would shift like it was in 4lo but be in 2wd high.. So before you got goin good you would be in o/d and the converter would lock and the truck almost go dead.

its prolly your problem or I guess it could be the switch but that was more common in 99-02