4WD not work diagnosing tips?

I have an 03 Tacoma with the push button 4WD but it doesn't seem to be working.

When I shift the leaver between N 4L and 4H I can feel the gears mesh so I have power going to it.
Also when I hit the button the engine RPM drop slightly and I can swear I can hear a whiring sound before the RPMs go back to norm. So I would assume the electronics are working.

However when I hit the gas on a dirt road I only get wheel spin from one of the rear wheels.
Anyone know what my issue could be?

 

I would have a friend look at the front driveshaft (crouched beside the truck) and watch for it to spin when you pull forward (slowly) with the truck in 4H or 4L.

If it doesn't spin start looking at electrical connections on the transfer case.

If it does spin, then you've ruled out the transfer case and need to inspect your ADD actuator on the front diff.

 

Is this happening in both 4hi and 4lo?

Is the green 4WD light lit up on the dash instrument panel?

 

Enough weight on the front axle to not break traction would be my guess.

spinning wheels don`t move the truck!

Then maybe your doing a full launch high rpm and dumping the clutch from a dead stop??

Curious to see how this plays out.

 

Sorry for the late reply on this one.
I pushed the 4WD button and waited a few seconds while in park and drove forward. The shaft coming out of the transfer case going towards the front axel did not move.
I would assume this is the electronic bit located on the transfer case is not engaging anything?

Quick update. With the key on (without engine on) I can hit the button with a stick and my finger on the actual unit. I do feel a slight pulse. Could this mean this part is working properly?

 

Your first test where the front driveshaft didn't spin means it isn't working properly. Feeling that slight pulse sounds like it's trying to. Next step is probably to crack open the actuator on the back of the transfer case and see why it won't engage. May just be full of gunk and need a good cleaning

 

Will do. I did notice that the plastic around each screw was cracked. Not a great sign.
Just for my knowledge. Does that actuator also move a mechanical piece within the transfer case to engage it, as well as spin the electrical contacts?

 

I know it does move a mechanical piece to engage the front shaft, not sure it spins electrical contacts though. I think the pin that it actuates has a screwing type action as it engages/disengages

 

Ok I understand a bit better. The electric motor spins a worm gear which spins this disc. (This spinning disc moves a shaft in and out to engage and disengage 4WD?) And the contacts on the disc align with a circuit on the cap which communicates its position or (drive mode) to the computer.

 

So you should be able to hit your 4wd push button with the key turned to the accessory position (as you did before) while it's torn apart and troubleshoot why it isn't engaging.

 

Will do.
Now should I touch the disc/shaft part to see if that will engage/ disengage by hand or is that not a good idea?

 

That should be fine. So long as you put everything back together the way it was originally. Taking pictures before pulling stuff out is usually a good idea