4HI light flashing- Won't shift into 4x4- FIXED

Hey all, I've been exploring the forums for a while now and haven't posted much but I wanted to share my experience fixing my 4x4 system. I had some trouble finding info on what to do so I figured I could share my experience and help anyone else who has this situation in the future. My initial problem was that when I selected 4hi the light just flashed and I could not hear the normal click into 4x4. I went home and crawled underneath the truck and saw nothing out of the ordinary. I disconnected my battery and unplugged both the ADD actuator and the transfer case actuator, waited a while, hooked the battery back up and still had the same problem. After doing some research I found that its fairly common for the front ADD actuator to cause people issues. One diagnostic test I found was that if it was the FRONT actuator, the front driveshaft would be able to rotate when put into 2hi. This was not the case in my truck and other forums indicated that I had a transfer case issue. I use my 4hi at least once a month so I figured it was not the transfer case or I would have had issues shifting into 4hi before it failed altogether. I figured my problem was in the back actuator and started looking for obvious breaks in wiring or cracking on the vacuum hose. I couldn't see anything from the outside but when I gave the vacuum hose a slight tug, it popped right off!

This hose was obviously shot, so I went and bought a replacement to see if that fixed the issue. No dice

After doing some research I found a video linked in another thread that eventually got me to my answer.
https://youtu.be/TmuEVv1neVQ?si=R-w11O95B5kC-nP1

I decided to take apart my transfer case actuator and found that it was full of dirt and very corroded.


I scrubbed it with a wire brush until it looked like it was mostly metal and applied some dielectric grease. I made sure to clean around the whole thing thoroughly before I put it back on the truck. Another note, make sure to check the contact points on the part of the actuator still attached to the truck, mine were full of grime and looked much better once I cleaned them off a bit.

After a test, 4hi and 4lo both worked! This was a huge win and saved me a bunch of money getting it diagnosed/fixed by a mechanic.

I hope this helps!

 

Glad you got it fixed! Is that a vacuum line? Or is it the breather? Trace it up to the engine compartment and see if it terminates in a breather cap on the firewall.

 

It's the breather hose which a lot of people find degraded/cracked, allowing outside elements in.

I check mine every time I grease the driveline and throw a little 303 on it. I've considered replacing it entirely, after 15 years, it's probably overdue on something I doubt costs more than $20.

@Brayblade good find on the actuator cap. We post that video on most of the threads here related to 4HI flashing issues. I usually point people over here: https://www.tundras.com/threads/4wd-issues.119382/#post-3081795