4WD Doesn't Engage on Manual Transfer Case

[tcbaklash]

Having an issue with getting 4WD to engage with my manual transfer case on my automatic tranny-equipped SR5. I've tried shifting in to 4L and 4H while stopped in drive, stopped in neutral, stopped in low gears, and rolling in drive. 4WD light on the instrument cluster does not come on. I did hear a gear grinding noise while attempting to get 4WD engaged while driving up a hill.

I got the vehicle in working order late June but haven't needed to even turn 4WD on until a couple weeks ago, so I don't know if it worked before. Tranny w/o transfer case was recently replaced, maybe it's unplugged from the harness? I won't have much info until later when I can get under the vehicle. My other assumption would be a solenoid or other actuator traveling half way (especially considering that I heard gear grinding) and not engaging 4WD and not hitting some kind of limit switch that turns on the 4WD light.

 

[Tyler James Inc]

Your tcase switch might be unplugged- or not working.
If it's a manual tcase, you are engaged to the front diff, but your ADD shift fork isn't getting actuated.

 

[tcbaklash]

Finally got around to checking plugs on the tcase. Everything looked to be in good condition. I have the tools and everything to swap out the tcase but I want to avoid spending the $300 at the junk yard for another, is there anything else I can check here? Any small parts that could need replacement?

 

[gamefreakgc]

Finally got around to checking plugs on the tcase. Everything looked to be in good condition. I have the tools and everything to swap out the tcase but I want to avoid spending the $300 at the junk yard for another, is there anything else I can check here? Any small parts that could need replacement?

If yours has it, check the 4WD VSV (vacuum-switching-valve) in the engine bay to make sure all the vacuum lines are connected. If someone ever disables it, it's usually there since the engine bay is easier to access.

If you have the push button 4WD, I don't think it has the VSV.

 

[tcbaklash]

If yours has it, check the 4WD VSV (vacuum-switching-valve) in the engine bay to make sure all the vacuum lines are connected. If someone ever disables it, it's usually there since the engine bay is easier to access.

If you have the push button 4WD, I don't think it has the VSV.

Finally got around to checking the VSVs. Neither one will actuate but the front diff and the transfer case work mechanically if I put the "red" hose on a vacuum line. I'll be back after I do some voltage checks and more reading.

 

[gamefreakgc]

Finally got around to checking the VSVs. Neither one will actuate but the front diff and the transfer case work mechanically if I put the "red" hose on a vacuum line. I'll be back after I do some voltage checks and more reading.

If they are not working double check the hose routing and just snatch a new set from the junkyard. They are tricking to diagnose correct operation and it requires the Factory Manual to figure out how.

 

[tcbaklash]

If they are not working double check the hose routing and just snatch a new set from the junkyard. They are tricking to diagnose correct operation and it requires the Factory Manual to figure out how.

Considering that there is no voltage on either VSV plug in 2WD or 4WD, I'm not going to replace them just yet.

I used to have access to Chilton Database when I remembered my library login lol

 

[TheDurk]

Finally got around to checking plugs on the tcase. Everything looked to be in good condition. I have the tools and everything to swap out the tcase but I want to avoid spending the $300 at the junk yard for another, is there anything else I can check here? Any small parts that could need replacement?

Did you test the T-case switches switches electrically? "Looking" at them is less than useless. Good ones and bad ones look exactly the same.

 

[tcbaklash]

Considering that there's been a lot of work down there before and after I bought it, checking the plugs on the t-case was very important for my situation. It's had 3 trannies and 2 transfer cases so far.

I feel like an idiot because I was missing the 4WD fuse. I'm an electrical worker so this is especially humiliating. Dropped in a fuse, everything functions but no 4WD light. I read somewhere about a limit switch or sensor in the front diff but I've no clue where.

 

[phattyduck]

On the manual shift case you have 4WD engagement goes like this:

Shift from 2WD to 4WD (lever from left/top to left/bottom). This should close a switch on the transfer case, which will engage the ADD relay in the passenger footwell, which will swap power to the two ADD VSVs under the hood (one should always be powered with the engine on). This moves the vacuum actuator on the diff, which then closes a switch that lights the light on the dash.

If you aren't hearing a faint click in the passenger footwell when you move from 2WD to 4WD, then the first suspect is the transfer case switch. Hopefully [MENTION=10169]TheDurk[/MENTION] can point out which one is which (there are 3 switches - 4WD, Neutral and Low)

You can can also do a quick mechanical check by comparing the front driveshaft in 2WD vs. 4WD - it should not move by hand in 4WD but should be free in 2WD.

-Charlie

 

[tcbaklash]

On the manual shift case you have 4WD engagement goes like this:

Shift from 2WD to 4WD (lever from left/top to left/bottom). This should close a switch on the transfer case, which will engage the ADD relay in the passenger footwell, which will swap power to the two ADD VSVs under the hood (one should always be powered with the engine on). This moves the vacuum actuator on the diff, which then closes a switch that lights the light on the dash.

If you aren't hearing a faint click in the passenger footwell when you move from 2WD to 4WD, then the first suspect is the transfer case switch. Hopefully [MENTION=10169]TheDurk[/MENTION] can point out which one is which (there are 3 switches - 4WD, Neutral and Low)

You can can also do a quick mechanical check by comparing the front driveshaft in 2WD vs. 4WD - it should not move by hand in 4WD but should be free in 2WD.

-Charlie

Relay clicks, everything works. 4hi, 4lo, switching on the fly, etc. Just no 4WD light.

 

[TheDurk]

Considering that there's been a lot of work down there before and after I bought it, checking the plugs on the t-case was very important for my situation. It's had 3 trannies and 2 transfer cases so far.

I feel like an idiot because I was missing the 4WD fuse. I'm an electrical worker so this is especially humiliating. Dropped in a fuse, everything functions but no 4WD light. I read somewhere about a limit switch or sensor in the front diff but I've no clue where.

Look on backside in the center. You can see the harness going to it in this pic:

 

[phattyduck]

Here's another pic, though no wiring. The switch is visible as a two-pin grey plug just to the right of the front diff flange here:

The switch may be bad or it might be unplugged at the switch or right above the diff flange (follow the ADD VSV vacuum lines down from the VSVs to find that plug).

-Charlie

 

[tcbaklash]

Thanks guys. I'll tackle it once I find a Runner in a junkyard (it's been pretty dry lately...)