Valvoman

Trying to diagnose my 4x4 system not engaging. It's a 1993 manual 4x4 w/ a 3.0.

Here is what I've done:

1] Switched 4x4 lever to 4H. Check front driveline and it does not spin.

2] Switched 4x4 lever back to 2H and front driveline spins.

3] Tested continuity of both VSV's [passenger side wheel well] Continuity!

4] Checked all vacuum lines. Good!

What is next?

A] Pull the the ADD lever housing thing?
B] How do I check for vacuum at the ADD?

Thanks...

scope103

You mean, when you're driving down the road? Then your problem is in the transfer case, not the front differential.

You may have enough friction in your front differential to spin the (unrestrained) front driveshaft in 2H as you're driving down the road. But when you shift to 4H, something is grabbing the front driveshaft (probably in the transfer case) and the differential friction isn't enough to turn the driveshaft. And your ADD is not engaging.

The front driveLINE goes from the transfer case all the way to the front tires. I assume you mean driveshaft.

You can test for vacuum with your thumb; just pull off the line in question and put your thumb on the end. But if the driveshaft doesn't turn in 4H (as you're driving), then your problem is not vacuum related.

RJR

I read the OP's post as saying he crawled under the truck and tried to turn the drive shaft by hand and got the results he posted - in which case the problem likely is ADD related.

I would suggest checking vacuum at the diff. I assume the green 4WD light isn't coming on. The light is the last thing in a chain of rvents that goes: transfer case in 4wd, switch in tcase closes ADD relay under dash, relay switches vacuum solenoids on passenger inner fender, vacuum moves actuator in front diff, actuator closes indicator switch, indicator switch lights green 4WD light.

Valvoman

That's right...I crawled under and tried to turn it....no light.

This thing is frustrating. Lots of little things must go right to make it work.

RJR

I have poor internet service right now, but I wrote a post in the last two weeks with more detail about how to troubleshoot the ADD system. See if you can find that. I think it was titled "my truck is trying to kill me".

scope103

Here's Ron's posting. https://www.yotatech.com/forums/f116.../#post52307652 I can't improve on it much.

Valvoman

Thank you!


With engine off, ignition on, move the transfer case back and forth between 2wd and 4wd. You should hear the relay click under the dash. If you don't, you have a relay or transfer case switch problem.
- If the relay clicks, raise the hood and listen on the passenger side as someone moves the transfer case lever. You should hear the vacuum solenoids clicking on the fender.
- If those work, start the engine and pull the output vacuum lines (the ones that go to the diff) off the vacuum solenoids. Put your fingers over the open vacuum solenoid ports, have someone move the t-case lever, and note that the vacuum changes from one port to the other.
- Finally, trace out the vacuum hoses to the differential and make sure they are healthy and connected.


I am not geting the relay 'click' when the key is on (and the engine is not) when i move the lever from H2 to H4. I assume it is about the same 'click' as when i turn the radio on and the antenna goes up/ down?

So, should I pull the t-case switch and check that fiirst for continuity? Or, start w/ the relay? Anyone know the part number?

My pickup has 164,000 miles btw. Prob never was put in 4x4 before i got it.

scope103

This might help. http://web.archive.org/web/201204242...26addcontr.pdf

I would start with the switch on the transfer case. The relay is just a SPDT relay 28380-44030, but it has a less-than-standard pin-out.
http://www.toyotapartsoverstock.com/...838044030.html
http://web.archive.org/web/201204242...26addcontr.pdf

They relay is not as un-protected as is the switch on 4wd shifter.

Valvoman

I pulled the T case switch, cleaned up and check for continuity. It's okay.

I cleaned the connector contacts as well with electronic cleaner. Reinstalled, checked the wires etc while under there (nothing frayed or destroyed).

Went ahead and put the ignition switch to on (but engine not running)....and no click.

Is the next step checking the under dash relay??? And do you have a procedure?

Thanks for helping me guys. This is actually enjoyable.

Valvoman

I went ahead and pulled the relay from under the dash.

I took jumpers from the battery and placed them on terminals 2 and 6 on the ADD. It clicked!

So, why is the ADD not clicking over when I turn on the key (to accessory) and drop it in to H4?

What is the next step? Anyone?

scope103

Use your multimeter. Do you have 12v on pin 6 of the relay socket with key-on? Do you have ground on pin 2 with the transfer shifter in H4 or H2? You say you confirmed the switch on the transfer case; if you don't get ground at the relay, then you know where the problem is in the wiring.

RJR

Three possible causes:
1) The wire between the ADD relay (green/white wire connected to pin 2) and the transfer case switch is broken. Thus the ADD relay never knows the tcase went into 4wd.
2) The wire supplying 12V to the high side of the relay coil (brown wire connected to pins 1 and 6) is open, thus no power to the relay coil. That wire gets power through the 10A gauge fuse. Are your gauges working? If so, that fuse is OK.
3) The ground wire from the tcase switch isn't actually connected to ground.

You'll need your multimeter to find out which is the problem. If you don't have one, go to Harbor Freight or your nearest hardware/auto parts store and pick one up. Should be less than $10 for an adequate one. A multimeter is an essential tool for any electrical problem, and can save you hours of swapping parts.

I would do these steps.
1) Pull the green/white wire from pin 2 of the ADD relay. With the tcase in 4hi, check for continuity from that wire to ground. If no continuity, the problem is 1 or 3 above. Next check the ground wire on the tcase switch for continuity to ground. That will tell you if the problem is between the ADD relay and the tcase switch, or between the tcase switch and ground.

2) If the ground side is good, check the brown wire connected to pins 1 and 6 of the ADD relay for 12V with the key on. If that's missing, work upstream until you find the break. The brown wire goes to the "integration relay" which isn't a relay at all but rather a big junction box in back of the fuse panel behind the driver's kick panel. That's the source of its 12 volts.

Valvoman

Thank you RJR and scope103! I will do what you've suggested.

To note, gauges are fine and 10A is good. However, yesterday when I was poking around, the fuse blew...no windows, locks gauges. Weird. Replaced it today.

It's odd, because this truck has not been hacked at all - zero aftermarket mods...

Valvoman

I went ahead and did 1 above. There was no continutiry between pin 2 and ground. However, there is continuity between the tcase switch connector and ground.

Also, I checked pins 1 & 6 for 12V. 12V is there.

There is a ground issue somewhere....

RJR

So that means the green/white wire is broken between the relay and the tcase switch. Time to look for something that either got pinched or burned off against the exhaust pipe.

Valvoman

Thank you for the help. Ill run it down the next few days.

Hope this thread is helpful for someone in the future.....

nv4runner

You need to do that test with the key in the ON position, but without starting the engine. It should also click when the engine is running, but you might not hear it with all of the other sound an engine makes.

RJR

Good catch, nv4runner. I missed that he had only turned the key to accessory. Looks like his later test was valid, however, since he had 12V on the high side of the relay.

nv4runner

It sure sounds that way to me too.

If I were doing the testing I would check for continuity between the green/white wire and the transfer case connector at this point, just to positively identify the wire as the open in the circuit.

Valvoman, what is the resistance reading across the transfer case switch when the T case is in 4hi? Anything over .5 ohms may give the system problems.

Valvoman

Sorry, i had the key set to on, but engine not running.