4-High Not Engaging

Hello my friends,

I believe my 4-High is not engaging. My truck has routinely gotten stuck this winter (heavy snow in Utah) even when switching to 4-high, and it’s been pretty frustrating.

I just tested out again, and I am pretty sure it’s not engaging. No front tire spin or traction. The dash light indicating it’s on does shoes, and it does not flash. in addition, I can hear the 4-low engage when I switch to this (there’s an audible noise) and I notice a difference in driving.

What are the common failures that result in the 4-high not working? Hoping for some common ways to test to fully confirm it’s not working / identity the problem…..also please send good vibes my way.

 

Check if the front driveshaft spins in 4wd high. If it doesn’t, open up the transfer case actuator and clean the contacts. If it does spin, then it’s your front diff actuator.

 

The driveshaft was spinning. What's the best way to determine if the whole actuator is bust? or just the wiring?

 

Do you have a copy of the FSM (field service manual) for your truck? It may have something in there about how to diagnose it. If it doesn’t you can certainly get the electrical diagrams to determine where the power is coming from and the signal to engage it.

Do you use 4wd regualrly? If not, then lack of use exercising it is most likely the cause.

 

Check this out: https://www.tundras.com/threads/4wd-issues.119382/#post-3081795

 

There is a vacuum line that goes to the actuator on the transfer case. It can come loose or get cracked from age or dislodged from a car wash. It is rubber so it is pretty vulnerable. You might check underneath and see if that is still in place.

Edit, you said 4 low was working, it might be electrical with the button itself.

 

I'm pretty sure 4LO requires successful engagement of 4HI + being in Neutral to engage? I might've missed where OP said 4LO was working above. If 4HI isn't working and 4LO is, that sounds more like the 4WD ECU is borked to me.

 

This is my understanding as well.