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View Full Version : No 4wd light on dash, no 4wd even when transfer case lever is moved to 4HI or 4Lo



bikerjosh
12-19-2011, 04:30 PM
Posted this on two other forums, with no success. All I want for christmas is my 4wd back.:coffeedrink:


Ok having an issue with my 4wd on my 98 SR5 4runner. Stats: 3.4, AT, standard transfer case (no push button multi mode). Noticed a month ago when I went into 4Hi the dash light did not come on; about a month prior went a 3 day offroad trip and the system worked flawlessly. Figured it was just a burned out bulb, since I was traveling around 50-60 on fireroads and truck seemed pretty stable. This weekend in a dirt parking lot I wanted to see if the 4wd was engaging, so I put the lever in 4hi, and broke the tires loose. The person outside the car said only the rear wheels spun. Iíve read a few threads about similar problems but they usually involve the push button transfer cases and involve blinking lights, versus no light. Checked & replaced, (even though it looked good) the 20 amp fuse in slot 22 under the dash, but no change. Looking underneath the car I see the one plug that goes into the diff with the wire harness, and the two vacuum lines. Is there a way to test the switch on diff w/o removing it? Looks pretty tight. Any good next steps?
If there is a good write up on this please send it my way.
Thanks Josh

Owyhee H
12-19-2011, 04:52 PM
Sounds like your Automatic Differential Disconnect(ADD) is not working. I know there are some writeups on troubleshooting the system but i have no personal experience with it. I have seen one case where the person switched the old vacuume actuated ADD for a newer all electric ADD, there are many opinions on which is better. I would start by checking the vacuume lines really well to make sure there are not breaks. If the lines cannot activate the ADD then no light will iluminate.

pray4surf
12-19-2011, 07:57 PM
Locate the VSV (ADD Solenoids) components (maybe below/behind the battery) and unplug and replug the wiring connectors - I had a loose one once..

Still nothing, one at a time, pull the vacuum lines off the ADD Actuator and find out if you get vacuum. If nothing, try moving the selector lever (in the cab) - make sure that you get vacuum in either one (but not the same) line with the in cab selector in both positions.

Use this diagram to help troubleshoot
http://www.tacomaterritory.com/forum/attachment.php?attachmentid=1785&d=1127245249

Also, When you engage 4WD do you here the ADD Relay 'clicking'? This relay is found in the passenger-side footwell, behind the kick-panel.

bikerjosh
12-19-2011, 08:43 PM
thanks pray4surf .
I'll look for/ check the ADD solenoids. No clicking in the relay behind the passenger kick panel. I did pull that off some time ago when I was looking for a spot to remount my FTC box for my 7th. Wonder if I could have knocked something loose?
thanks again

Dave Bennett
12-19-2011, 08:50 PM
Locate the VSV (ADD Solenoids) components (maybe below/behind the battery) and unplug and replug the wiring connectors - I had a loose one once..

Still nothing, one at a time, pull the vacuum lines off the ADD Actuator and find out if you get vacuum. If nothing, try moving the selector lever (in the cab) - make sure that you get vacuum in either one (but not the same) line with the in cab selector in both positions.

Use this diagram to help troubleshoot
http://www.tacomaterritory.com/forum/attachment.php?attachmentid=1785&d=1127245249

Also, When you engage 4WD do you here the ADD Relay 'clicking'? This relay is found in the passenger-side footwell, behind the kick-panel.

Great post.

tanglefoot
12-20-2011, 05:21 PM
The ADD only disconnects one of the front half-shafts? Does that mean that you can't put a full-time diff locker in the front unless you get rid of the ADD?

bikerjosh
12-20-2011, 07:39 PM
Ok, so after work last night I managed to get a some time to look over the rig and find out some stuff.
I can confirm the relay on the passenger side is clicking, so I got that going for me.
Disconnected and reconnected both the blue and brown harnesses dirty on outside, but both were well seated and clean inside. The outer cases of the solinoids look pretty beat up. Is there a way to check them? Checked the plastic one way valve (blue in the picture) and it is still functioning one way.
79015

Close up on of solenoids
79016

The ADD indicator switch looks pretty tough to get to w/o cutting a wrench apart. Took the picture from a funny angle since you can't see the wiring from the bottom..
79017

Thanks Josh

shinyblackdeer
09-16-2013, 12:43 AM
Sorry to drag this thread up from the depths, but did you ever solve this problem?

onewyr
03-16-2014, 01:41 AM
I just happened to find this page/site while trying to troubleshoot the exact problem as the original poster. The diagram in the post was very helpful and I found out purely by a fluke of luck that there is a bundle of grounds bolted to the driver side of the intake right next to the diagnostic port, while I was checking the solenoids with the truck running i bumped this group of grounds and heard the solenoids engage/disengage. I tried cleaning the grounds but that didnt fix the problem so i made some modifications to the diagram to show how i wired in a dash switch to control the front diff. Here is the pic.
http://i2.photobucket.com/albums/y23/onewyr/1998%20taco/updatedschem.jpg (http://s2.photobucket.com/user/onewyr/media/1998%20taco/updatedschem.jpg.html)

In the original setup the relay coil is engaged by switching the ground, this wasnt gonna work for the lighted switch i wanted to use so i grounded that wire that went to the transfer case switch and then put the new dash switch inline between the coil and the fuse. Going this route still allows the dash light to work and i have full control over the diff. Now i can disengage the front diff if i want to without taking the truck out of 4wd yeah i Know it doesnt sound like a big deal but this is what i did to get my 4wd working.