4wd Light Doesn't Turn On 4H
 

Hello all,

I have a 1999 SR5, manual transmission, 206K. 2" suspension lift. Car runs great, no problems shifting, nothing. I bought it about a month ago. The only potential issue is that when I shift into 4H the 4wd light does not turn on, but it does when I go into 4L. And the car is definitely in 4L (pretty easy to tell). Any ideas? Any simple ways to tell if I am actually going into 4H? Thanks

Do a slow speed turn on asphalt and you will feel it bind up in 4H very easily. Not recommended to use 4H on aspahlt, but a quick test won't hurt it.

Odds are your 4h sending switch, or its wiring, on the TC is bad, since 4L is operational and ADD thus is known to work. Common fail--it happened to me.

I couldn't tell doing the turns in a parking lot so I took off the rear driveshaft and did it that way. 2H works great, 4L works great, 4H does not engage. Any thoughts? Also sorry for my ignorance but what is 'ADD'? Thanks all!

Ok, figured out ADD. So never mind on that.

Just confirms what I said before: 4H sending switch on TC.

Thanks TheDurk. I'll get to it when this Charleston weather clears up! Much appreciated.

Got under the car this morning before the rain started back up. You say the 4H sending switch is the one that went on you, looking around sounds like a pretty common (and sweet for $36) fix. I just wanted to make sure I was looking at the correct switch. From what I've read it should be the switch towards the rear of the drivers side on top of the TC. When looking down at it I can see it with the shifter cover off. Is this correct? I deleted the diagram as it was incorrect.

I suspect that's the wrong diagram. Don't you have a J-shift like I have on my 1999 5-speed? And aren't there two switches on the top rear of the TC? One on the left and one on the right? I forget which side is which but the one you want (H4 detection) has a solid blue wire. The L4 switch has a blue wire with red stripe. You should test the H4 switch for continuity when depressed to be sure it has failed before you spend your $36. Sometimes you can clean them, but you never know how long that will last.

That diagram you posted is from the 2002 manual. They did not have a J-shift or a 5-speed in 2002.

TheDurk, you are spot on again. Drivers side has the solid blue wire, the blue with red stripe is the passenger side of the TC. Cleaned it and got nothing. Checked continuity, the switch is dead. This should be an easy fix. I really appreciate your help. I'll let you know how it goes.

OK! To follow up on everything I cleaned the 4H sending switch and everything is working great now. For anybody in the future who needs new sending switches, the Toyota dealership in Charleston was incredibly unhelpful. So the part number I got for this switch is 84222-35080. I also found another part number that seems to be the same thing, I can't figure out the difference and it's 84222-35110. I hope this helps somebody else. TheDurk, I really appreciate your help. Happy wheelin.

Ok back again...unfortunately. I was mistaken, no 4H yet, light still does not come on in 4H only (not even flashing). Tested the old 4H sending switch i replace again and it WAS bad, thinking this might be a few things. So here is what I have so far.

1. New 4H sending switch, issue out of the way.
2. Disconnected the vacuum lines by the battery under the hood as TheDurk suggested in another post. In 2H nipple A has vacuum and nipple B does not. In 4H IT IS THE SAME nipple A has vacuum and nipple B does not. In 4L they switch (as they should but don't in 4H), nipple A does not have vacuum, nipple B does have vacuum.
3. When in 4H the front drive shaft is not able to be spun by hand.
4. And yes I did switch the 20A fuse with another one to test it, no change.

By the way took out the 4L sending switch on TC and cleaned it just for the hell of it.

Well, great progress. This is down to a wiring issue. We know both the VSV and the ADD control relay work because they are good in L4. So it is either the blue wire between the relay and the H4 switch, or the ground wire to the H4 switch does not have ground.

So put truck in H4. Then check if the white/black wire on the H4 connector has a good ground. Check the blue wire also has ground with truck in H4. Check that connector very carefully to be sure both wires are making a good connection, especially on the truck side. Clean it with contact cleaner. Then pack it with dielectric grease.

If it is definitely passing ground at the H4 switch, then check the blue wire for ground at the ADD control relay in the passenger kick panel on Pin 2.

One of these two places has to NOT show ground. Which one will tell us where to look next. My money is on that truckside connector at the switch on the TC. The rest of the circuit is just not too likely to fail.

Ok done, black/white wire has good ground 0.8ohms but blue wire has no ground (super high resistance). What is this telling me? Wish i had a schematic for this thing! Once again, thank you for the help.

Blue wire has no ground where and how? At the relay, at the switch, with switch connected, in H4...? Please be a little more precise. Or, if you can read the schematic, be my guest:

Sorry, the blue wire has no ground at the connection for the switch that I replaced ("Detection Switch (Transfer 4WD position)" in the diagram) on the wire coming from l11 in the diagram. So looking at the schematic I'm thinking that narrows it down to the ADD indicator switch, the combination meter (not sure what that is) or the ADD control relay. What are your thoughts?