SUCCESS!!! Durk you are the man I cannot be more appreciative for all of your help. After running all tests I was able to back track everything back to the 4wd transfer case actuator. So I removed to cover to the actuator limit switches like one member did earlier. It was fairly clean inside but water did get in there at on point and left some build up. Cleaned everything inside, applied new dielectric grease everywhere and replaced the large o-ring to the cover. While doing this I also discovered that the little seal in the actuator connector had been folded backwards and was keeping the connector tweaked in such a way that it would make intermittent contact and allow blinking light conditions randomly or when wet. I fixed the seal, used dielectric grease on all remaining 4wd connectors. Now everything is perfect. Soaked the truck under low pressure everywhere, no issues, high pressure, no issues, washboard roads, no issues. So, my issue is officially fixed thanks to this group! 👍👍

 

Howdy everyone!! Hope everyone's 4wd is working as it should. Mine is not at the moment. I have a 99 4Runner ltd with the rear locker. I tried using my awd by pressing the m/m button on the J shifter and I only got blinking lights. So I started with some testing of switches. Found that the front diff switch was bad along with the forward position switch that is on the t case actuator. Both switches are the same style plug. Got both switches in and replaced. Still have the same issue. I can power the actuator in awd and I get the 4 green tire lights on the dash. No blinking. I then go for h4L and lights start flashing again. After reversing this process, back to h4 and then press the m/m button I still have flashing lights and it will not come out of awd. I did some probing with the 4wd Ecu unplugged and the vehicle in 2h and found I had 12v at pin 6. I unplugged the the harness from the diff sensor. Checked again and still have 12v. If I unplug the abs Ecu I lose the 12v. Is this pointing to a bad abs Ecu or does it ground through L4 transfer case switch? My only worry is that I haven't even gotten to L4L yet. Thanks for any additional info and for all the info you guys have put in this thread.

 

The switches signal by closing to the white/black ground wire which is the second wire on all the detection switches. Pin 6 is the Diff Lock detection switch which sends its signals to both the ABS ECU and the 4wd ECU. What you describe is exactly what I would expect. So far, it's looking like a TC actuator issue, possibly the Diff Lock Detection switch. Leave it in h4L, unplug 4wd ECU and check for GROUND at Pin 6. Do the same in AWD and 2wd. Should have ground in AWD and 2wd, but not H4L. If you don't pull switch and check function.

 

I'll try this tonight when I get home from work. Should I put it in h4L without the m/m switch depressed? And the diff switch should be the one an the actuator that is toward the front of the vehicle? This switch is brand new. It was bad to begin with. If this is the correct switch, I do have 12v at pin 6 with this switch unplugged. That's what made me wonder if the abs sends this signal back if l4 switch is closed.


And I have already swapped transfer cases. I before the factory test method with the relay to check the actuator. The actuator did nothing, which made me believe it was bad. I haven't performed this test yet with the replacement case cause I think there is still another issue. But I guess it's possible I have two bad ones.

 

I am not an expert on the m/m TC as I have a J-shift 5-speed. But I am real good with a circuit diagram. I believe it makes no difference how the button switch is once you go into H4L, but I would accept clarity from anyone who knows.

If you are going to insist that it can't be this and it can't be that then don't bother troubleshooting. I am expecting to rule the switch out, but I'd feel real stupid if we pulled the actuator and it turned out to be the switch all along. More important is to confirm the switch is sending the correct signal, as in the pieces inside the diff are depressing the switch contact, or not.

We have one of three cases, I think:
1) the 4wd ECU is not signalling the actuator,
2) the actuator getting the signal but is not locking the center diff
3) the diff is locking but the 4wd ECU is not getting the confirmation signal.

Does that sound right to you?

 

I just got home from work, put the vehicle in hi4l. I have 12v on pin 6 to ground. I unplug the sensor. Ohm connector. It's not closed. Check voltage again at pin 6 to ground with sensor unplugged. Still have 12v to ground. I only lose 12v to ground when I unplug the abs Ecu.


Update. With abs Ecu unplugged. Diff sensor unplugged. 4wd Ecu. Test from pin 6 to ground and I have 12v to ground. Looks like I have a pinched wire somewhere. At least that's my guess.


Just found all three switches at the top of the transfer case are bad. Cannot get any of them to close. Seems odd but the vehicle does have 232k on it and I'm sure 4wd wasn't used that much.

 

All three switches are bad? Yikes. Good thing you never got to checking L4. Are you relying on the common ground they all share? If so, recheck just for continuity of the switch itself using OHMS.

As for the rogue 12V+ in the Pin 6--red/black wire, I got nothin'. Does it show 12V+ at the ABS ECU and at the diff switch connector, too? I'd check that, just for fun. Is it there with the key off? That might give us some clues. It can't be true 12V+ or a fuse would pop when the diff switch closes. What ground are you using?

This is a fun one.

 

I'm checking basic operation of the switches. I have the transfer case pulled out since the used one I have is leaking. So that's when I used my meter for work to check continuity of each switch.

 

OK. Three bad switches it is. Please keep me posted. I love this stuff. Weird, huh?

 

Tell me about it. Missed two wheeling trips now. Parts are on order from the dealer.

 

Finally got this pig fixed today.

First and foremost. Don't pull apart the actuator. If you decide to pull the center section out of the actuator, make sure it is put back in exactly the same spot.

My case was in H4L. After checking the plug on the actuator it though it was in H2. So I got things clocked right now. And everything works.

 

Found 4 bad switches and replaced them with factory parts. The other two switches test perfect on an ohm meter.

Confirmed that my front actuator works and all vacuum lines hold vacuum.

Rear actuator moves in and out when power is applied with a battery charger at 2amp.

Drained old fluid and replaced with Lucas synthetic.

Swapped 4wd computers.

I don't know what else to check. Any ideas? So sick of this blinking indicator and missing trips because I never know when I'll be stuck in 2wd, or 4wd. Very frustrated.

 

I do have one brand new sensor/switch from Toyota, and a known good 99 4wd ECU for sale, just in case anyone who reads this thread needs some parts.

 

@WhiteKnight1130, when you say you removed the cover, do you mean the black cover held on with three screws? Or is it the motor cover with 4 bolts? I've heard removing the motor cover will cause the gears to pop out and I don't know that I'd be able to get everything timed right and put back in.

I've done everything short of pull the transfer case and those two covers.

Thanks!

 

@Adkins, how were you able to check the plug on the actuator to determine what position the actuator was in?

I'm wondering if I haven't moved mine manually with a battery charger so many times that I may have it in the wrong position.

 

This is what I used to determine the position of my actuator. I was in h4L but the actuator was reading h2. Hope it helps.

 

Thanks! That's a big help. I'll check that connector with an ohm meter tonight.

 

When i bought my 99 3rd gen I put in in 4 wheel drive right away and it got stuck. I freaked out, but luckily I went with the least expensive and most likely culprit which was the diff actuator. Glad you got her fixed up!!

 

So using this, I was able to determine that the actuator indeed goes to all positions. However, when in any 4wd position, the indicator light just flashes.

Another question to those that have moved the actuator by applying power directly to it...does it always engage / disengage smoothly?

Sometimes I can hear the actuator move, but rather than clunk into place, it just binds and groans at the end. I have to move it back and forth reversing polarity a bunch until I get lucky and it pops into place with a loud bang.

I'm wondering if something is bent inside the case and causing all these issues. I did accidentally hit it with 10 amps instead of 2 amps once and it moved faster, but I can't image that damaged anything; hope not.

 

I moved it with the case shifted to neutral. Never had an issue with it binding.