TOD Failure

I've got a 99 Trooper with TOD. Winter before last, the 4WD quit working and the dealer replaced what they called the "control valve". It was under a
cover mounted right on the front center of the front axle/(differential?). It was covered under warranty. Now, after only being used about 3 times since, it supposedly failed again. It doesn't work and the "Auto" and rear wheel lights flash slowly. This time, the dealer and the district customer service manager say it is not part of the drive train and is not covered under the 60/60,000 drive train warranty. I've owned the vehicle for 48 months and it has 47,950 miles on it. The mechanic at the dealer told me that these things hang right out there in the front, exposed to rain/snow etc. and can easily fail. I wondered about that since it is behind a baffle and, I think, inside a pretty sturdy outer cover. However, the district customer service manager says it is highly unusual for this valve to fail and really unusual for it to fail a second time on the same vehicle. He asked if the mechanic had done a continuity check. I didn't know, since I originally thought this valve was a mechanical thing. But the district customer service manager says it is just a solenoid operated control valve. He suggested taking it for another opinion to another dealer. I told him there are no other dealers around so he suggested a GM dealer. We talked about the fact that the Troopers are made in Japan and I got the impression that the TOD is a GM design and though parts may not be interchangeable, a GM trained mechanic should be able to diagnose and even fix it.
Question is, what do folks here know about this? Does anyone have experience with this valve failing? Or can an electrical connection come loose? If so, where are the likely places for such connections to have a problem - under passenger seat, somewhere on the front of the vehicle, etc.? Can GM service departments at least check the thing out - in other words, even though the Trooper is made in Japan, is it similar enough to the Rodeo, for example, that a GM service department would know how to check it and maybe repair it? If I can't find a mechanic to check it, is there an external electrical access point where I can do my own continuity check. If not, how and how difficult is it to open the covers and get at the valve itself for a continuity check? Is there a gasket that might need replaced? This mechanic at the local Isuzu dealership was done in about 2 minutes and spent the rest of about 10 minutes getting the part number and price and writing up a report form. So I don't think he did much at all. In fact, after I left the dealership, I noticed he had left the 4WD button depressed and in the dealership parking lot, I noticed that the 4WD worked perfectly for a while. After getting on the highway, I turned it off. But then, when I entered the large, snow covered lot of another group of stores and pressed the 4WD button again, it did not work again, the green "Auto" light began flashing slowly and then the red "Check" light came on. That was the first time I've ever seen that red Check light and I've not been able to find out what it really means. The book says to stop the vehicle and turn the engine off. It went out right away when I turned the 4WD switch off. When I turned it off and the Auto light went out also. The next time I tried to turn it on, the same thing happened, so I've left it off.
I hate to be paranoid about this or distrust the mechanic or dealership, but something about it doesn't seem right, particularly after the comments from the Isuzu customer service guy.
Thanks for any help,
galb accr at earthlink dot net - take out the spaces and convert the at and dot to the usual for direct contact
Chuck Galbach
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I have had a loy of problems with TOD on my trooper.
The type of oil in the front axle is critcal.
Also have a look at what I posted.
www.lssolutions.demon.co.uk/Car/4wd.htm
David

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I have had a loy of problems with TOD on my trooper.
The type of oil in the front axle is critcal.
Also have a look at what I posted.
www.lssolutions.demon.co.uk/Car/4wd.htm
David.

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Any information I give is not guaranteed to be accurate and based on my Trooper a 98 3.0l Turbo Deisel imported into the UK from Cyprus. I am also working from memory. Check out note I put on the web and posted previously http://www.lssolutions.demon.co.uk/Car/4wd.htm .
It has a 4WD drive switch rather TOD.

On my trooper the solenoid valves are mounted on the front axle. Whilst there is metal plate under them they are not enlosed, the wiring is extremely thin and the vacuum pipes unsecured. They are unacceptably vunerably for a 4WD.
However, the district

Mine did.

It is possibly because you haven't used them much. The failure on mine was due to corrosion inside one of the valves.

On my trooper the valve is electrically operated.
But the district

If you are practical, get underneath, remove the front axle protection plate (4 bolts 14mm head (I think)). The solenoids are located on the front axle near the centre. They are connected to by two vacuum pipes to a metal protrusion which is a diaphram. Applying vacuum to one side shifts it one way and engages the front axle, to the other side disengages the front axle.
MAKE SURE YOUR WHEELS ARE BLOCKED HAND BRAKE ON AND THAT YOU ARE SAFE TO WORK UNDER THE VEHICLE WITH ENGINE RUNNING. HAVE NOTHING ON LIKELY TO GET CAUGHT IN MOVING PARTS ETC.
Disconnect the power plugs to the solenoid.
To check the voltage ignition need to be on. TOD/4wd switch off.
Measure the voltage across the two pins of the plugs. I believe the solenoids should be powered when in 2WD so you should get 12V or more. Check both plugs. They both derive the +12V from the same output on a control card. (See web link for location)
If you have voltage on both plugs try switching TOD on. Voltage should go.
To check the valves. it is easier to remove them although it can be done in situ. (Two nuts) but LABEL THE PIPES AND MAKE A NOTE OF HOW THEY ARE ATTACHED. One pipe will be more difficult to pull off because of vacuum.
With the valves on a bench use a 9Volt battery with a couple of flying leads. Apply to the pins of the socket on the solenoid yopu should hear a click, clean the vacuum pipes and try blowing through them, it is change over valve you should be able to blow in through one of the pipes and with the solenoid not powered it will come out of one pipe, with it powered it will come out of the other.
If you think a valve in sticking you may be able to strip it down and clean it up. See web link.
I told him

As above and Web Link
Or can an electrical connection come loose? If so,

On front axle. On control box (see web link for location)
Also on my Trooper the earth (0V) used to come down the wiring harness but had been cut and connected to chasis adjacent to the solenoid valves.
- under

On mine it was very easy once you are under the car. Access to the control box inside the vehicle is not difficult either, just fiddly.
This mechanic

Same as at mine.
and spent the rest

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