So...

'98 Limited auto with the push button 4wd on the side of the shifter, i hit the button and no 4wd light comes on the dash. T-case actuator works, front driveshaft to the front diff engages.

VSV on driver fender has vacuum in 2wd and test light confirms power to the solenoid with vacuum, push the 4wd button on the shifter and power and vacuum stay on the 2wd VSV - it doesn't switch to the other VSV.

So... if it doesn't switch that means either a transfer case indicator is bad or the ADD relay is bad. Is their a relay for the auto trans 98? the 99's have the relay by the glove box, the 98 supposedly doesn't have one since it's an auto? is that correct?

Front diff indicator doesn't have a chance to work because the front diff never gets engaged, so that means what transfer case indicator do i need to check? their are 2 next to each other towards the top of the t-case on the driver side, one was blue (fwd) the other was dark colored (mud covered). Should i just replace them if i'm even bothering to cut a wrench up to get them out?

I'm tired, it's late, long week, thinking skills clouded by a few coffee stouts. I'm going to bed, please provide input.

You really need to PM The Durk. He's the expert on this sub-generation of 4wd system. Luck.

What happens when you try to go into 4L with the T/C shifter? Is this a J-shift?

You have no relay. ADD is controlled by a 4WD ECU. In '98, should be in driver's side kick panel according to the attachment below. They are rarely the problem unless truck has been submerged.

I know it's a pain, but ideal is to test all the T/C switches for continuity, which means removing them and testing with an Ohmmeter as you push their buttons. They ain't cheap, and I'd hate to replace good ones. It's probably the 4wd position switch, high on driver's side of T/C, shown as #9 in diagram toward very end of attachment. If 4L works, this is almost guaranteed.You never know what mice have done to the wiring, it happened to me.

Attached Images

ELECTRI2.PDF (4.43 MB, 461 views)

It's a push button 4wd. I think you're right, only way to really know is to pull them and test. I doubt it's the ecu, everything else works except no signal is being sent to the vsv to engage 4wd.
Thanks for taking the time! I appreciate it.

-Rock

There can be j-shifts with the pushbutton. What is the pattern on T-case shifter? Straight line or J? And as I said, check 4L. It tells you a lot, one way or the other.

Straight not j, high or low does not matter. No signal to tell the vsv to switch, no lights on dash, t-case locks the front driveshaft in no matter what.

Unfortunately, the exact input logic of these 4wd ECU's is not contained in the Toyota manuals. We have to guess. I know, in my case, a failed 4wd switch killed 4H but not 4L. But I have a 5-speed J-shift with no button.

I can't look at the EWD and say there is a single switch that would cause your symptom set. Still, I think testing all those switches on the T/C is your next best step. A failed ECU is rare so I'd confirm all inputs first.



Here is your '98 EWD:

Attached Images

4WD w 2?4 SELECT SW.pdf (88.3 KB, 271 views)

Fixed. 4wd indicator switch 84222-35110, blue plug sensor (not gray) on upper driver side transfer case. Had to cut a slot in a short 1 1/16 short socket for the wiring and 3 wobble extensions with a short one on the socket to follow the curve of the transmission tunnel. Easy job. Thanks the durk!

Thanks for the detailed feedback. I really appreciate it because it adds to my understanding. The blue one is plug D4 on the wiring diagram I posted which is labelled as Transfer L4 Position Detection Switch. No way would I figure that switch caused both H4 and L4 to fail to engage the ADD. You would think it would only break L4. Bizarre. Just means I will keep telling folks to test ALL the damn switches instead of trying to pinpoint which one from the symptom set--which I feel I SHOULD be able to do. But it rarely works that way. Logic gets it wrong more often than right.

4WD Transfer Indicator Switch
The one I replaced is the switch that tells the vsv to engage the front diff, the gray one next to it is the 4L switch. I found a link with a good explanation. The gray switch tested bad and my 4L indicator doesn't work, not that it's worth $80 to know I'm in 4L. I also posted the part number wrong, it begins with an 8 - 84222-35110

Well, if that's true the '98 EWD is wrong. Which is certainly possible.

If you had a diff lock you would want that L4 switch as its engagement is required for the diff lock to engage.

It could not be the 4L switch because the rear diff locks in 4h.

I thought it was supposed to engage only in 4L, unless you mod it. (I don't have one.) Is there any chance you have those switches screwed into the wrong holes? The '98 EWD says:

Blue plug = 4L
Grey plug with green/red wire = 4wd
grey plug with red/green wire = neutral

I'm thinking the top two might be switched. The plugs wire up only one way, but you can screw them into whatever holes you want. (I know: "That's what she said...")

Unfortunately, I can't be sure which hole is correct for which switch from the manuals I have for '98. I just have the EWD.

The plug on the harness is the same color, blue for blue sensor and gray for gray sensor. I can only tell you what I know and what I've seen researching my issue. I think the blue one is the position indicator to tell vsv to engage the front diff. The gray plug tested bad and I don't have an indicator for 4L. I don't have have to be in 4L for rear diff lock, I can lock it in 2H (that's how I got out of the river when my 4wd stopped working) I'll take some pics later or tomorrow below the truck

Then it's definitely been modded or the switches are screwed in the wrong holes. One or the other. It's not supposed to do that. But you're probably better off the way you are unless you get a good grey switch.