Magic 4 wheel drive

[IT-Engr]

I have been plagued with an unassisted automatic 4 wheel drive engagement at highway speeds (60-75 MPH) on a 1999 GMC Jimmy. The Vacuum Switch has been replaced twice with the Stainless Steel Switch. It now has no engagement of the front axle, the Transfer case engages the front drive shaft but the axle will not engage (Possible Shift Collar Damage). If I try to manually engage by pulling the cable, only a grinding noise occurs. If I try to select 4 Lo, The 4 Hi & 4 Lo lights flash back and forth. Is there a diagnostic I can use to test the Encoder motor and Electronic Control module? I realize I will have to replace part in the Front Differential but, I am tired of being 300 miles from home and having the front axle engage. I have also experienced NO 4X4 in cold-Snowy weather, a reset of the system by disconnecting the battery has restored the 4 wheel drive. Has any one had similar experiences and resolved them? Please share your success or failure with me. This vehicle has been a real POS, I have owned many Chevrolets, one GMC and they seem to share some common failures. My last GM vehicle ever.

 

[PhoenixZorn]

This vehicle has been a real POS, I have owned many Chevrolets, one GMC and they seem to share some common failures. My last GM vehicle ever.

Not going to get many responses - that you'll like to hear - with a comment like that... However, if I were you, I'd take this over to the IFS forum...

 

[dremu]

This vehicle has been a real POS, I have owned many Chevrolets, one GMC and they seem to share some common failures. My last GM vehicle ever.

Then buy an old one with a freaking LEVER on the floor and be done with it

-- A

 

[sled_dog]

you need to get wiring diagrams and figure out how the system is controlled. Sounds like an intermittent short somewhere. If you have experience with it, get a diagram, a multimeter and go at it. if not, I'd say turn it over to a professional cause the wiring may just end up being a nightmare for you.

If a push button tcase is locking into 4 wheel without your knowledge, why would you possibly think it is the vacuum actuator on the front diff?

 

[IT-Engr]

I have tested the switch

Thank you for responding. I have tested the switch. I am trying to determine if there is a diagnostic procedure to test the encoder motor and the electronic 4wheel drive module in the right kick panel. This has been a random activation, twice in the last two years both in the month of May. There have been many other issues with this vehicle (catastrophic transmission failure @ 61000 miles, Heater core explodes @ 71000 miles, left door pops every time it is opened due to bushing failure), the local dealer was reluctant to work on it during warranty as I did not purchase it from there.

 

[stus84]

dremu Quote:
Originally Posted by IT-Engr
This vehicle has been a real POS, I have owned many Chevrolets, one GMC and they seem to share some common failures. My last GM vehicle ever.
Then buy an old one with a freaking LEVER on the floor and be done with it.


I special ordered my 2002 daily driver with the lever on the floor. They are out there but are hard to find.... 2002 Chevy 5.3 1500 4x4 extended cab Z71. 70,000 + without a problem

 

[sled_dog]

month of may leads me to believe you live somewhere like PA where it rains alot at this time. Would likely be a bad connector or stripped wire in that case. Really going to have to crawl around and check all the connections. I have no personal experience with this setup, just telling you what I would do.

 

[IT-Engr]

Thanks for your comment

Thanks for your comment, but the Jimmy is only manufactured with the electronic control. There is no option or conversion to a lever. The best thing about this vehicle is the fuel economy (20+ on the highway) and the ride. otherwise it has been less then reliable. When you spend $35,000 for a vehicle it should be reliable for more than 36,000 miles. You have a 1/2 ton pickup and I am sure you are pleased with it.

 

[NJBLZ]

. When you spend $35,000 for a vehicle it should be reliable for more than 36,000 miles. QUOTE]

You would think so, but nothing could be farther from the truth these days. You thought you were actually going to get your money's worth? come on, stop joking around.



Someone I work with had a brand new 2004 GMC 1500, it would go into 4-LO while at highway speeds. The truck, (and I use that term loosely) went back and forth to the dealer many times, always returning home with the same problem. The dealership eventually bought it back.

 

[hunterguy86]

Posi Loc?

I have seen those posiloc systems advertised in fourwheeler in there unending numbers of adds(gripe for another time). I wonder if that would work for this persons situation or if it is even applicable. I just wanted to throw that idea out there. You guys with more exprience chime in on this.

 

[sled_dog]

he already has that, the problem is the Tcase not the axle engagement.

 

[IT-Engr]

Clarification of Axle engagement

I do not use a PosiLock, I am still using the original Vacuum control. I have disconnected the engagement cable to prevent another episode of engagement at Highway Speeds. The reason the Vacuum switch has been replaced in both instances is due to the recommendation of a GM service depertment technician at two different locations. They contend this is a common failure and is due to the switch binding up internally. I beleive there must be some relationship between heat buildup after prolonged interstate driving (3-4 hours) and the encoder motor. I live in Southeastern Illinois and my son is in school at NKU (next to Cincinnati, Ohio). The drive there is 3 1/2 to 4 hours depending on traffic. I have to help him move in May or June each year. I also have to drive to Chicago several time each year but there has never been a case of engagement possibly due to having to stop at the half way point for my wife to shop.