Question about 2001 Isuzu Trooper

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4x4 tod not engage

Isuzu trooper 2002

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YES, as Tanner 78 has said, it was the Vacuum Switch Valves (VSV) (well, T78 said 'vacuum sensor valve' but I''m sure he's talking about the same thing)

The VSV's are tiny little things, one grey and one blue. They are made of plastic and are each about the size of a Bic lighter. They're mounted together on a thin rectangular metal plate which is then mounted onto the front axle, and there is a skid plate that protects them.

Each VSV has a solenoid inside it...a solenoid is an electrically operated device that moves a little internal plunger back and forth. In this case, the plunger sends 'vacuum' to either the RIGHT side or to the LEFT side of the vacuum device that "engages" or "disengages" your front axle.

In my case (as it turned out) the little plungers inside the solenoid of the VSV's must have been plugged up with something...gunk... oil...I don't know, but they were obviously not doing the job.

HERE IS HOW I FIXED MY TROOPER FOR FREE: I cleaned out the VSVs. Simple as that.


1) Remove the VSV's from the front axle. EASY DOES IT! There are three little black vacuum hoses running to each VSV...they are a pain to remove, and BE CAREFUL because the body of the VSV is PLASTIC and if you break buy a new one. The hoses just slip over the little have to pry them off gently with a straight blade screwdriver. However you do it, remember you're dealing with a tiny plastic part. ALSO, be sure to note where the hoses came off! LABEL THEM!

2) ELECTRICAL: You also have to remove a little electrical wire from each VSV...the wire connects with a colored plastic plug (one grey, the other blue). There is a TINY brass wire that locks this plug onto each VSV. You have to GENTLY pry this wire up to let it clear the little locking lug. It's a pain...make sure you have good light. And again, it's plastic, so take it easy.

3) When you have the hoses and wires off, remove the little nuts that hold the thin metal plate to the axle. The whole assembly...which is about the size and weight of a pack of cigarettes...will come right off.

4) Remove each VSV from the metal mounting plate.

5) Where the electrical wire connects to the VSV, you will see there are two 'spades', or little brass ears where the plug went on. You need to get two little jumper wires with tiny alligator clips on each end, because you have to apply battery power to these VSVs to test them.

6) Hook up the jumper wires to the spades on the VSV, then place one clip on the negative post of your battery and one on the positive. If the VSV is working, you should hear a very tiny CLICK from inside the VSV. You might have to hold it right against your ear.

7) If it makes a click, it's working OK. Test it a few times.

8) If you get NO click, the plunger inside is plugged, and you need to clean it out.

9) Use a SOLVENT BASED electrical cleaner and spray it into end nozzle of the VSV. CAUTION: Do NOT use a greasy spray like WD40 or anything like that, or you will gum up the VSV and it will be useless. Make sure you use a solvent based spray that completely disappears when it dries. Spray some into your hand and let it dry...there should be NO residue or oil on your hand at all.

10) Now it's a matter of 'spray and shake' and hooking up the wires to the battery to listen for the CLICK. Spray the cleaner into each of the generous with it... If you have some compressed air, shoot that in too...just get the gunk out. You might not see a huge pile of **** come flying out...we're talking about a small device here.

11) If you get to the point where each VSV makes a nice, clear CLICK every time you apply the battery power, you're done. Reinstall everything and it should work. MINE DID! First try...the front axle engaged, and it works fine months later.


Posted on Jan 10, 2009

  • Orest Walchuk Dec 23, 2012

    Thanks Wesley! I followed your recommended procedures, and after about four hours under the 2000 Trooper had my TOD light back to normal, that is solid green drivetrain lights lit, and no red check TOD light blinking. I believe it is fixed, but will wait until the snow tomnorrow to really declare final victory. In the meanwhile, I took the part number off the VSV assembly it was Denso Part No. 8-9710185-1, I think. No luck finding it on the web, yet. Thanks again! - Orest

  • Orest Walchuk Dec 23, 2012

    Thanks Wesley! I followed your recommeded procedures for repairing my 2000 Trooper TOD problem, and after about 4 hours under the front axle, was able to replace everything (though very rusted down there) and sure enough when I engaged the Four Wheel Drive button on the console, the previously blinking CHECK TOD lighht did not appear, and the green drivetrain diagram showed as should be, constant lit rear wheels, and partial lit front wheels. I will await the snow tomorrow to declare full victoiry, but so far so good. Thank you very much for your advise on this matter! Orest


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Hi Wesley,

I had the same problem this week. Used your procedure and got the VSV "clicking" in minutes.
Lacking a spray, I used solvent and injected it with a seringe. Needed to gently tap the VSV with a small hammer for initial movement.
Thanks a lot!!!!!!!!!!!!

Posted on Jan 02, 2010

  • jer4999 Jan 02, 2010

    Tapping the VSV will also work for diagnostics.

    The VSV's are located on the front of the left front axle. You need to remove a cover to get to them (2 bolts wrench 14).


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Thanks for this solution. In my case the valve was stuck pretty good but I let the solvent soak for 3 days spraying break cleaner into the vsv ports every 6 hrs or so and finally whatever was in there was dissolved away and I could hear the valve clicking when I apply 12v. Reassembled everything and blinking tod check light was gone. Again thanks to WesleyByron for the detailed solution.

Posted on Jun 23, 2012

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Need vac diagram for 4 wheel drive from axle to motor and anyplace elsr it hooks up ? please

TOD system , LS body.??????

ever google for it
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look in web.;/images and videos.tabs
tons of facts free
google is friend
or use mitchels and read
log in and read a near FSM book on YOUR car.
i cant guess PT if car is TOD, only you.

i guess car was basket case or hacked up?
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you need to use google
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lots more google can in fact find every singla real isuzu forum on earth, and is best
there. real forums.
fixya is last change garage,,,,,,,no order here.

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