Hello, My 01 Trooper won't engage the 4wd. The lights blink then go to the red CHECK light blinks. I had recently had the tranny rebuilt because torque converter was failing. The tech there has searched all the codes in all the appropriate units and the only thing he could find was that the ABS system MAY have a fault, but he could not find anything definitive. He thinks maybe that the front ABS wheel sensors tell the TOD when to apply power to the front wheels and that may be why the auto 4wd is not engaging. I have looked and looked for something about this but so far nada. I would appreciate if anyone has had similar problems and was able to remedy them to let me know.. ANY info will be greatly appreciated
Alex

 

Take it back to the tranny place. Tell them it worked fine until they messed with it, and be adamant about it. I would also call a few other tranny places and see if they ever had a similar problem, or any suggestions.
The answer may be something simple, like a bad electrical connection or difficult, like a spring or valve. Maybe they put something together wrong.

 

My 01 Trooper was doing this...failing to engage the front axle when the dash button was pressed...the 4x4 symbol would flash but the axle would not engage. I fixed it for FREE.

The problem was the two VACUUM SWITCH VALVES (VSV) that move the front axle in and out of 4 wheel drive. If you get under your Trooper and remove the bottom skid plate (about a 10" x 10" metal plate located under the transmission) you will see the VSVs. They are two plastic devices, each about the size and shape of a Bic lighter, located side by side. Each VSV has several small black vacuum tubes connected, as well as a small wire harness.

The VSV is an electric device that control the vacuum to the front axle. My problem was that these VSVs were gummed up and dirty inside and would not supply enough vacuum to pull the front axle mechanism in and out of place.

What you need to do is REMOVE each VSV and clean it out. This has to be done VERY carefully because they are flimsy and fragile, and EXPENSIVE to buy!! SO don't break it! The VSVs are mounted on a thin metal plate...you have to remove the plate, then disconnect the vacuum hoses from each VSV. BE CAREFUL!! I cannot state that enough. Draw a little diagram of the VSVs and the hoses, and label each hose so you get them back in the right place. If you get the mixed up you are sunk.

Removing the electrical connector is also tricky, as it has a small brass wire that must be pried gently up to release the plug. Again, be very careful. If you try to force anything, you are in trouble. (Make sure you're working in a clean, dry location and are warm. There is no way you will be able to get the patience and comfort to do this properly if you're laying under the vehicle in the snow.)

Then, take some carb cleaner (NON GREASY...Do NOT NOT NOT use WD-40 or anything like that...make sure it is NON GREASY!!) and spray it into the body of the VSV. You can take a tiny jumper wire and connect the electrical contact of the VSV to your car battery and you should hear a small "CLICK" inside the body of the VSV. That means the solenoid is working. Keep spraying the carb cleaner into the body of the VSV, keep cycling the electrical solenoid, and you should get it working fine. You want to hear that CLICK each time you touch the jumper wire to the battery.

Then, replace the VSVs, connect the wires and hoses, and you should be good. Mine front axle engaged BETTER than new (faster) after I did this, and it cost me the price of a can of carb cleaner. If you go to the garage it will be many hundreds of dollars I am sure.

Hope this works for you.

 

Thank you im going to try it this weekend !!

 

I would not use any kind of solvent (like carb cleaner) on the inside of the VSV's.
It will cause the rubber diaphram inside to dry rot sooner.

 

sorry to bring back an old thread. I've been trying to fix my non engaging 4 wheel drive problem for several years. It's a 98 Trooper. At first I thought that it was the VSV, so I replaced with a known good one, but once I replaced it, it made no difference. Checked all voltage and vacuum, but still nothing. Then for ****s and giggles, reversed the 2 vacuum hoses coming from the front axle to the blue and gray VSV. Would do you know. It works. The only thing is that when in 2 wheel mode, the 4 wheel indicator light on the dash constantly flashes. Any ideas why?

 

Does it stop flashing in 4WD?
Are you sure it's actually in 2WD?
Check the switch on the actuator that sends a signal to the ECM saying the front axle is locked.

 

Yes, the flashing stops when in 4WD and yes 100% sure its in 2WD. Tested both on a lift. All 4 wheels spin in 4WD and only rear wheel spin when in 2WD. Tested while driving as well and definitely feel the difference between the 2WD and 4WD.

 

There's a switch on the front axle actuator that tells the ECM the axle is locked or unlocked.
In the t-case there's a motor that moves it in/out of 4WD. And there are switches to report to the ECM that it's in 2WD/4WD. Possibly one of those switches are not working properly. One could be showing the t-case to be in 2WD but the other not saying the axle is in 2WD, etc.

 

’98 Isuzu Trooper

Problem:
Going from 2WD to 4H to 4L,and back again ,is not possible. Once engine has warmed up (5-10 minutes running) pushing Shift On The Fly button on dash will not engage into or out of 2WD or 4H.

I have taken to ‘reputable mechanic’ three times and they believe it has something to to with ‘4WD module’ (word they use for small black box located somewhere in dash) I have had them replace said part (3 times) and it still does not work after car has warmed up.

Any suggestions are greatly appreciated and please be very specific. I am a beginner and not a mechanic.

Thanks,