Hey All, Ive got a 2000 trailblazer 4X4(S-10 model) with push button 4WD. When I push the 4hi or any 4WD button I hear what I think is a relay panel click somewhere in the passanger side of the dash and then what I think are the hubs locking in, however the light on the dash never lights up solid Instead it blinks. On top of this I dont feel like Im in 4WD. In the past I have gotten the button to light up solid but only in 4L, during these few times I have felt like I was in 4L. Is there any way to troubleshoot this problem or verify the 4WD is engaged. Also if anyone can tell me the proper way to lock it in to 4WD meaning should I stop completely and be in Neutral or just push and go. My truck is an automatic, not sure if that makes a difference. Any help would be greatly apreciated. Thanks for your time.

 

You should always be in neutral to go into 4LO as this is a range change in the transfer case (lower gear). Sometimes it helps to be rolling slightly when trying to go into 4LO, but for the most part, stopped is the preferred method. For a mode change (2HI to 4HI or 4HI to 2HI), you do not have to be in neutral or even stopped.

Being a Trailblazer trimmed Blazer, you likely have the NV236 transfer case (4-button with Auto4wd option). If so, this is particularly bad for the DIY'er as it requires a Tech2 or equivalent scan tool to access the TCCM and check for codes. The system is also much more complex.

I would start by checking the operation of the vacuum actuator located under the battery. If you have the NV236 transfer case, the actuator will be controlled by an electronic switch on the firewall. This switch should open and allow vacuum pressure to the actuator to pull on the engagement cable. If the cable does not fully engage the front axle, this can cause the incomplete shift, resulting in the TCCM shifting back to 2HI.

An incomplete shift may also be caused by a faulty or failing encoder motor on the side of the transfer case. The encoder motor is responsible for the actual shifting of the transfer case. It has a 4 channel position sensor (the encoder) which reads the position of the shift motor to ensure proper positioning during a shift. If it looses signal to one of the channels, it will revert back to 2HI.