My Truck: my 2001 4Runner SR5 has an automatic trans and the 4wd lever with the push button on the side of the lever to engage 4wd.
Truck has 252k miles on it now.

My issue: truck seems to slip into a neutral mode while driving with 4wd engaged .

A couple of times now, i've pushed the 4wd button (4H) at about 15-20 mph, and the lights blink in the dash as normal while it goes into 4wd, and I believe the 4wd is engaged. Proceed to heading downhill in a coasting mode (in drive, at idle) on a dirt road, the entire system acts like its in neutral, vehicle coasts to a stop. The trans is in drive, and i've not adjusted the tcase lever, only ever pushed the 4wd button, i can't remember the status of the lights in the dash. Moving the trans in and out of gear and moving the tcase lever from 4Hi-4Lo makes no difference, engine revs but isn't moving the wheels. The only thing that "fixes" it is to place the trans in Park and restart the vehicle. Two other times i've heard a gear grinding noise and then a "clunk" and it goes into 4wd, but haven't experienced the loss of forward motion.

Yesterday, engaged 4wd Hi, drove along a dirt road and the road got pretty rough (for a dirt road), and near as I can tell the vehicle "bounced" out of gear, loss of connection between engine and wheels, coasted to a stop. Placed vehicle in park, restarted (touching nothing on the tcase) and vehicle was fine. Vehicle behaved fine for the remainder of trip.

thinking this is some kind of sensor issue, but really don't know. Any help you can offer would be appreciated.

 

Do you have the multi-mode transfer case with the 4x4 shift lever that goes 2Hi - 4Hi(locked center diff) - N - 4Lo and then a button on the side that gives 4Hi but not locked t-case?

It sounds like the actuator either isn’t spinning far enough to fully engage or the gears are worn allowing it to jump out of gear. I’d lean more to the actuator not engaging far enough.

First I would try taking the round cover off the actuator and cleaning the contact traces inside.

 

thanks. I'll do some digging on the threads and learn how to do that. what would you recommend i use to clean the traces?

 

Check out my build thread. I had a lot of issues with my 4wd system. I have pictures too. I sprayed everything with simple green to clean the old dried grease. Then I used some steel wool to clean the contact traces, then contact cleaner to get any hold out crud, and then dielectric grease to prevent corrosion from starting.

 

thank you, i'll take a look at your thread!

 

looks like I found my issue! I’ll clean this up and put it back together. May look around eBay and see if I can find this part!

The plastic neck on the connector seems broken!

Corrosion on pins

Yup…

 

The good news is the traces on the inside look nice and clean. Good luck on that socket.