Wont' go into 4WD sometimes... I replaced the vacuum hoses and still has trouble... electrical guy said he thinks it's an electrical diode in the transfer case that is going out... He's done work on our trucks a lot and has seen it before. I believe him because if I don't use the 4WD for a few days I have the problem, but once i get it going again it's fine. That tells me the connection has warmed up enough to work again. However, this won't last forever.


any thoughts? Is this fixable driveway? I hate electrical so I might just get him to do it!

 

Never heard of a diode in the transfer case. There is a switch in the transfer case that detects when you shift into 4wd and that switches a relay which then engages the 4wd vacuum valve to engage the front ADD. The switch should be easy enough to repace.
Read through this for more info
http://www.off-road.com/toyota/tech/add/

 

switch, diode whatever... I'm lost on electrical stuff... but I'm sure that's what it is because jiggleing the transfer case shifter helps...

 

The switch just screws into the side of the transfer case, I can't remember which side but it should have a connector with 2 wires. Check and see if the connector is tight. To check the switch put the transfer case in 4wd and check for resistance across the terminals. it should be zero ohms, and should be infinite with the shifter in 2wd. Maybe get someone to wiggle the shifter while you're checking the resistance. If the switch is bad just unscrew it and put a new one in.

 

Well, he is wrong. You have ADD? I suspect you have a 2nd gen Runner. Near the fuse box, you will see a blue and brown VSV, the brown gets you 4WD, blue gets you 2WD, make sure both are clicking (while in 2WD, unplug blue one, does it click) and do the same for the brown, except shift to 4WD. Are the vaccum hoses on right from the engine? Is the vaccum lines on right to the accuator? If they are backwards with ADD, when shifting into 4WD, you will get a quick green 4D light and then it goes out. Vacuum hoses fromt he engine come from 3 tubes, in a triangle shape, top one is #3, bottom toward back of engine is #5, and last one is #6. Air suction valve gets the #4 hose. Others goes to the vacuum tree als0 know as a "gas filter" on the schematic.