1999 with NV236 T-case Stuck in 4lo. lights at switch blink when pushed but default back to 4 Lo. Encoder motor and dash switch replaced less than 20K miles ago.

Tonight I removed the battery and checked the front hub locker vacuum
actuator under the battery. I don't have a gauge to check for vacuum so I pressed on it and I could hear air coming from the vaccuum connector at the firewall. The one that has 2 vac hoses and an electrical connector going to it. On the top is a small breathe hole about 1/8" in diameter that when squeezing the hub locker actuator the air was coming out of that hole. I assume that means that vacuum actuator under the battery tray is good?

Second, I removed the TCCM from inside the cab kick plate and noticed a bit of corrosion on 1 pin on the main "orange" connector so I carefully cleaned it and also sprayed contact cleaner on it and the other 4 spade connector, applied dialectric grease reassembled and no luck getting it out of 4lo. I can hear the TCCM "clicking" so does that mean it's working properly especially after cleaning and reassemble?

One other thought...has anyone changed the transfer case vacuum switch that sits on top of the transfer case? Could that be an issue on a 99?

Just thinking through possible causes for 4lo being stuck.

What about removing the front actuator at the front diffy? If it's stuck in 4lo can you remove and replace or does it have to be in 2Hi?

Sorry for the load of questions, trying to get this figured out this weekend.

I know the best thing is to get the TCCM codes read but it's going to be difficult to drive it to get it checked while in 4lo.

Thanks,

 

you could disconnect the cable going to the front differential thats connected to the actuator under the battery. That should release the front wheel engagement. Also you know the truck has to be in neutral when disengaging 4l to 4h. Dont believe the vacuum has anything to do with this. If its stuck in 4l it seems like it would be the t case. There is another electrical connection on the case on thr passengers side, you could check that also

 

Could be most anything, case, switch, TCCM, wiring, etc. There are no switches on the NV236. The only electrical device on the case is the encoder motor. You can manually shift the transfer case to 2HI after removing the encoder. You'd need to leave the encoder off while you drive to a shop to retrieve the DTC's. The problem is getting the encoder back to neutral. The case and the encoder MUST be in neutral to install the encoder. Shifting the encoder to neutral while it's off the case is difficult, if not impossible, without a bidirectional scanner. The brake in the encoder needs to be electrically released and the encoder electrically moved to exactly the right position, (neutral) simultaneously. There are several threads here on the forum that might help. Your best bet is to get it to a shop that can retrieve the DTC's and diagnose the problem.

 

Why do I feel dumb? Dont answer that please

 

Update...I was able to get it out of 4lo.

Here is what I did. I have a fairly long driveway on a bit of a downgrade towards the road. I started near the garage and once I got rolling, I shifted the tranny into Neutral and pushed about 2-3 times on the 4HI button. When it was blinking (and I was still rolling slowly) I put it into drive and it changed from 4Lo to 4HI. Once in 4HI I put the blazer in Park and pushed the 2HI button, it blinked a couple of times and went right into 2HI.

To make sure it had actually disengaged the front diff, I drove around and went to a parking lot and did a few circle with no issues. So, it is now back to "normal" in 2HI, but I realize it is unreliable. I would think the codes should still be stored in the TCCM. For now I will refrain from using 4wd, but I know something caused this obviously. Wondering what the problem is now.

Thanks for the help.

 

Are all four tires the same brand and size? None of them under or over inflated?


Take it in to a shop, ASAP, that can access the TCCM and BCM and have them retrieve the codes, then post them here. The codes will still be there if you take it in right away.