My truck had the ADD system. Well after I drive for like 10 minutes or so the 4wd will not work at all. There is no relay clicking when you move the transfer case lever and the 4wd dash light doesn't come on. After it sits for a little while or overnight the 4wd will work perfectly fine and the dash light comes on too. Anyone have this problem?

 

yep no what u mean i have the same prob,mine want ingage at the wheels.i think my probs is my air tank has a leak so theres no preasure to ingage:pig: but if its engages electrical i dont no what im on about.when u find out let me no please

 

I'm at work right now so I can't write a lot. Do a search for vacuum lines, they're a known cause of malfunctioning 4wd.

 

judging by the next page it is the vacum hose,mine had come off when i changed the plugs,However it still isn't working.Does the small air tank have to be full i have drivin 40ks and still not engaging but all other hose are fine and there is suction so whats my problem!!

jamie

ps excuse the pics had to try it!

 

fixed my problem.

the dam bulb had blown as well.