99 bravada awd problems

[taylerliberty]

at first the light came on said service awd. so took it to shop, and he put it on the computer and nothing.. the light is off. but it is still not shifting into awd.. i've talked to techs and said it could be the motor on the transfer case but thats 400 bucks. any ideas or is he right. i'd like to be able to find out before i have to actually put it in the shop on the big comp and pay hundreds to get it fixed..

[ivanhoe]

Originally Posted by taylerliberty

at first the light came on said service awd. so took it to shop, and he put it on the computer and nothing.. the light is off. but it is still not shifting into awd.. i've talked to techs and said it could be the motor on the transfer case but thats 400 bucks. any ideas or is he right. i'd like to be able to find out before i have to actually put it in the shop on the big comp and pay hundreds to get it fixed..

I have a ’99 Bravada with 80K. The engine was replaced due to an internal water leak at about 77K. Less than a week after getting the engine replaced the Service AWD light would come on from time to time when the car was first started. The dealer replaced the AWD module. A week later the AWD light started coming off and on again. At this time I had purchased an OBDII (with a Bravada you must have one) but when I plugged it in there were no error codes. When I took it into the dealer they said there were not error codes but they had found some in the history memory and thought the light was coming on because they did not clear out other old codes. Well at least I found out that my OBDII reader was ok. Well it is one week after the Bravada was in for the Service AWD light coming on problem and it started again. I just checked it with my OBDII reader and there were no error codes. Mind you the Service AWD was on. It goes back into the dealer in two days.

Did I mention we purchased the Bravada used with 32K and took out the 100K extended warrantee. The Bravada must have cost me at least 3K in repairs that were not covered and the insurance company may have put out about 15K at least. The warrantee only has a month or two on it and if there is something about to go with the transfer case or trans. I would like to try and get fixed under the warrantee.

I will let you know what they find out.

[njyahoo]

It's times like this that one has to dust off the old schematics (wiring diagrams) roll up the sleaves and start troubleshooting. Unfortunately too many people depend on computers to do that for us. If you can get your hands on a Haynes service manual there is a wiring diagram in the back with a troubleshooting guide. Tough part is finding someone who can read the diagrams.
DC is simple... current that leaves the + pole of the battery has to get back to the - pole of the battery. All vehicles use the metal chassis (body) as ground (- pole). So that means 99.9% of all wiring is attached to the + pole. The exception to this rule is generally green = ground = - pole. All current comes from the battery power source to a switching device (control) and then to the device being activated (load = lights, motors, etc) and then to ground. A short circuit is when power bypasses the load and goes directly to ground (blown fuse). An open circuit is when there is a break in the wire, the control fails, or you lost ground so the device doesn't get power. This is as simple as I can make it.
Now for your problem...since the computer has no stored code then you need to look at what would cause a disruption in the circuit but not cause an error. I would start with an intermittant problem like a loose connection either from the battery + post or to ground. You need a closed loop from the battery to keep things active. I would suspect something like a loss of power to the computer module that controls the AWD function. The symptoms would mimic what happens when you cycle the key switch off then on again. The dash displays flash to let you know they are functioning.
This is the best I can do without access to a wiring guide. I hope this can get you somewhere in the ballpark. One very important thing to look for first is a loose or corroded ground wire. 9 times out of 10 it's a bad chassis ground that causes the most intermittant problems in automobiles due to exposure to the elements or loose connections.