Hello All
my 2004 Envoy SLE the service 4WD light came on, does it just need the trans. case oil serviced? I have only owned it for a few months. First vehicle that I have ever seen that has 2HI, A4WD,4HI AND 4LO. (I am assuming that the A4WD is all wheel drive). No owner'* manual came with it. Any way i was going to service it next weekend, oil, filters, stuff like that. do you all think I should do the Diffs. and Trans, case while I am at it? If so what oil for the Diffs. and Trans case? I know the trans, take Dextron lll (says on the stick) does not look bad but do not know when it was changed last. 149K+ on the odometer. How to reset the SERVICE 4WD light? I know a bunch of stupid ???'* here but thought i would ask The EXPERTS.

Thanks in advance
MIKE

Most importantly, the owner'* manual:

The link: https://www.gmc.com/bypass/pcf/gma-c...k04envoyxl.pdf

. . . and I attached a copy to this post.

Next: Check out the following pages:

5-115 Capacities and Specifications
5-116 Capacities and Specifications
6-12 Recommended Fluids and Lubricants
6-13 Recommended Fluids and Lubricants
6-14 Normal Maintenance Replacement Parts
6-15 Engine Drive Belt Routing

Welcome aboard!

Oh yeah, the [Service 4WD] light could mean a few things, but a good place to start would be check condition and change fluid.

. . . and A4WD is Automatic 4WD. It locks the hubs then quickly engages clutches in the transfer case whenever it detects the rear wheels slipping under power. It uses a little more fuel this way, and also adds a bit more wear to the front drive components.

As opposed to true AWD where all of the wheels are driven all the time to some significant degree.

Thanks, How to reset the Service 4WD light?

If the problem goes away it will often reset itself.

By "problem goes away" I mean by itself (rarely reliable) or by repairing it (more reliable).

A good scanner could tell you more about the Service 4WD light, but sometimes it is possible to figure out what it is complaining about without a scanner.

Does the 4WD work properly? If not, what doesn't it do?

All works well, put it in A4WD and to 4hi , then 4lo and the light went out, so all is good there, one problem though, serviced all fluids, Eng oil and filter, Trans oil and filter, tTans case, Frnt diff., but when I went to do the Rear diff I cannot get the fill plug to come loose. 3/8 square drive but it won't budge I even went so far as to put my air 1/2" air gun with an adaptor and it will not come loose, retried with a 3/8 breaker bar and a little cheater pipe no luck. I know they don't use, left hand thread on diff plugs (don't think I have ever seen left-handed pipe thread) but that little BUGER will not come loose. So, all fluids are fresh except the rear Diff. I even tried putting heat to it for a while no luck. Any suggestions?
Thanks Mike

think i will look for a cover with a fill plug. really want to change the third hole, anybody know where to get one that will fit at a decent price? i guess i could go to a wrecking yard and get a cheap one and drill it and put a rubber plug like my dodge Durango has, just a plug grommet that Prys out with a flatblade then pops back in the hole, has never leaked or even weaped at all it is a 2003

I wouldn't use a rubber plug! Glad Dodge did it. I wouldn't.

The plug is standard thread.

For yours, I'd suggest getting something almost as big around as the plug, like a socket. Get under there every day or two and put it between the plug and your hammer and give it a couple of good whacks. Twist, and if it doesn't turn, give up for the day and repeat the same procedure again after you've driven it some more. It'* probably just never been taken out.

If you don't have seepage or leaks at the axles or the case I wouldn't touch it.

no leaks or seepage but I want to get the oil changed, found another cover with a fill plug, should be here today, so I will primer and paint it as it will come in bear metal form, so I will be able to change it from now on,