4.2 l 2002 Envoy 4x4 Question

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
Hi there, I had been all over Trailvoy.com, but that seems to be a dying site, for what I gather is monetary/politcal issues.

I do not wish to start more threads about this, because I have read so many, but do not seem to find the answer.

Long story short, I test drove a 2002 Envoy over the weekend and bought it without doing my due diligence.

I get it home, and realize the lights on the selector switch (4x4) do not light up, ever.

So I join trailvoy, read hundreds of posts, etc.

I already ordered a used TCCM from ebay. My question is though, most people with TCCM troubles at least get lets during Ignition.

It is also my understanding (due to your posts), that if the Computer does not communicate with the TCCM, it will throw a 4x4 service light.

However, I get no lights, ever (even after pulling #8 fuse), and NO service or check engine lights.

This may be totally unrelated, but the temperature control for the driver's side does not light up (just the red and blue scale), which is directly above the selector switch. The passenger side lights up, and the heat and A/C is fully functional - it is just the light that lights up the blue and red scale to select the temp.

I was a long time member of TCCOA (thunderbird and cougar club of america) until I totaled my Tbird.

It feels good to be back at a car forum, and I am forever greatful for the amount of time you have donated.

Do you have any suggestions as far as what I should check out or have checked out at a shop? It has a 150k miles, but drives like a DREAM!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
4 out of 5 lights on the switch are fed by the dimmable instrument light fuse. If they never come on at the lamp test time (ignition switch on before you start it), then the fuse may be bad or the wiring to the switch. The clue would be that you have MANY other lamps out such as all the window control switches and the rear wiper control switch. The "N" (neutral) lamp on the switch is fed by a different path, not dimmable, so could you confirm that lamp is also dark at the lamp test time? Perhaps your vehicle's previous owner was a scumbag with a dead 4WD system and they just pulled the connector off the back of the control switch instead of pulling the TCCM fuse because pulling the TCCM fuse would throw a code and illuminate the "Service 4WD" light.

Do you have any idea if the 50K transfer case fluid changes have been done? Might be an expensive repair. Do you have any recourse with the seller? Dealer/private party?

ADDED: A lamp like the other one you have out is just the lamp. If others in the same module work, then it can't be the module dimmable feed wire. IIRC, the automatic digital control module can be taken apart to change lamps, but not the manual one.
 

Sparky

Member
Dec 4, 2011
12,927
Welcome!

When my 02 Trailblazer's TCCM died, it did not light up the switch on ignition at all, nor did it throw a service 4WD light. It just didn't work. Basically the TCCM went to sleep and wouldn't wake up, but also wouldn't throw any errors. The way I confirmed it was my TCCM was to pull its fuse (I believe #48 in the rear fuse block under the seat), then put it back in. This forces a TCCM reset. In my case, this made the switch light up on ignition, but then go dark and the "service 4WD" light kick on, confirming the TCCM was toast.

I'll bet it is the same case with yours.
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
Ah! Good to know.

Roadie- no other lights are out.
Also, my 4x4 switch does NOT have a Neutral selection.
Just a4wd, 4hi, 4lo, and 2hi.

Should i pull #48 to test?
Used tccm will be here friday.

I have no way to know what was done. Private party sale.

Should I get transfer case flushed? Or is it risky to do if it has never been done?

Any other recommended services I should have done?

Thanks!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
DetroitSteel88 said:
Also, my 4x4 switch does NOT have a Neutral selection.
All mode switches have a Neutral position. Unmarked. Discussed in the Owner's Manual, unless 2002 was a rogue manual. You can easily find a 2003 PDF on-line.

Never put off a fluid service for fear it will do harm. That's a rationalization by folks who neglect their vehicles and don't want to change their ways.

Do the transfer case ASAP. Measure what comes out in case it isn't the expected 2 quarts. The private parts is not willing to share any service history? If they sold it as a 4WD vehicle and it clearly isn't one right now, you should have recourse for false advertising.

If you keep it, run a search here and do ALL 100K service. All fluids and spark plugs and transmission filter.
 

Robbabob

Member
Dec 10, 2012
1,096
DetroitSteel88 said:
Should I get transfer case flushed? Or is it risky to do if it has never been done?

Any other recommended services I should have done?

Thanks!

I think you'll be comfortable, as many will tell you: if in doubt at all, change all fluids and filters.

In your case, it won't solve your issue, but it will ensure you're starting fresh and documenting everything.

Good luck!
 

Sparky

Member
Dec 4, 2011
12,927
All switches have neutral but it is a "hidden" selection past 4LO that has no printing to identify it. A red N will flash briefly with the other (much brighter) lights at ignition when things are working properly.

You could pull the fuse, wouldn't hurt anything except give you that annoying light on your dash until the replacement comes in :biggrin: I would recommend pulling it while swapping the TCCM.

There is no transfer case flush (if someone says they can, don't). Just get 2 bottles of Autotrak II from the dealer (use no other fluid than this no matter what anyone else may tell you or you'll kill the case!), about $8-9 a bottle is standard. The drain and fill plugs use a 10mm allen wrench. Pull the fill first to make sure you get get it off before pulling the drain plug. It'll be tight so you might need to get a little creative to get enough leverage on the allen wrench unless you're smarter than I am and have a 10mm allen wrench socket that goes on your breaker bar. Don't try 3/8" allen, it is too small and you run the risk of stripping out the plug head. Just a small note, the bottles are liter bottles not quarts, so what comes out of the case will be a little less than 2 quarts.

Depending on the miles on the truck, other stuff is probably due. 100k miles for the spark plugs, front and rear differentials (standard 75w-90 gear oil, nothing special here), check the air filter and replace if it hasn't been done, fuel filter, etc. There is a list of stuff in the manual. Did you get a manual with yours or were you shortchanged on that?
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
Was shortchanged on that

It was an impulse Craigslist buy.
Guy knows little of cars.
He had it 6 months and lived in Phoenix so never played with 4wheel drive.

I have no knowledge of 4x4 but could rebuild a 4.6 litre Ford V8! Haha

The 4x4 world is completely new to me.

Thanks for all the replies. I will get on it.
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
Just pulled #48 under seat... nothing has changed.

Kind of worries me.
even replaced it with a spare fuse.

Is it possible the tccm is 100% dead or am I looking at an electrical issue?

Thanks
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
If the TCCM is 100% dead, the PCM would fail to communicate with it, and that would light the "service 4WD" light as I mentioned. Does your neutral red "N" come on during the lamp test time? If not, your cable could simply be disconnected from the back of the mode switch. That could conceal a lack of functionality for a reason we haven't been able to troubleshoot yet. .
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
Nothing lights up on the knob, ever.

Is there good directions on how to remove the knob without breaking a bracket?

It would be wayyy too simple if that was the fix! Haha

No lights EVER light up, and NO service engine soon lights, but the bulb works during test ( service engine bulb)
 

Sparky

Member
Dec 4, 2011
12,927
Does the "service 4wd" light come on briefly when you kick on the ignition?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Trailblazer 4WD switch removal writeup - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

I also had a thought that a connector that fell off the back of the switch would light up the "service 4WD light because of the switch circuit failing its diagnostic, but I never tried this to be sure it happened.

In our experiences here and on the OS for many years, a sleazebag owner is much more likely to kill a system and try to pass off a bad vehicle on an unsuspecting buyer, than to be honest about it. That's why a carefully-informed pre-purchase inspection is so critical.
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
I will check on my next break.

What area of the dash am I looking at for it?

If THAT bulb is dead, I will be a happy man because then it would mean that it IS my TCCM and not some funky electrical issue!

Whew! What a relief.

I am too excited to get the used tccm in the mail.

I am determined to get this figured out. It is my fault for not doing my research prior to the buy, and I know that.

He didn't seem smart enough to know how to take apart a dash and remove the SERVICE 4x4 bulb, there is just no way.

It is possible it died awhile ago, and since he lives in PHOENIX, never realized it because HE bought it from a shady guy. Who knows.

I hope the bulb is dead!!!!!

:smile:
 

C-ya

Member
Aug 24, 2012
1,098
Click the link I posted up above. After it opens, go to page 143 of the document (2-74 of the manual itself). This shows the location of the various lights.
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
Update - the service 4x4 does NOT light up during key on


Assuming bulb is dead.

Also, still no lights on selector switch at any time.

Could it still mean tccm dead?
 

Sparky

Member
Dec 4, 2011
12,927
Yeah. Since you already ordered a TCCM, and the 2002 TCCMs are known to fail, I'd just go ahead and swap it out when it arrives then go from there.
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
IT WORKS!!!!!!!!!!!!!

It took me 8 minutes to switch them.

I am such a dork, that I took it apart and put it back together before the new (used) TCCM arrived, so I knew exactly what to do when it arrived.


FOR FUTURE REFERENCE:
My mode selector switch NEVER lit up, even after pulling #8 fuse in engine block, and the 4x4 fuse under the rear driver's seat.

ALSO: At first, it would not switch into 4hi - it would only go into A4wd - but after driving around for a minute in A4WD, it allowed me to switch to 4hi, and it switched to 4lo when in neutral.

YAY!!!! Couldn't be happier.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
PM me if I can pay for postage to get your old one for a tear-down inspection. I collect dead parts,

Thanks for the report. Also make sure all your fluids get changed to keep it running well. The former owner can't be trusted.
 

DetroitSteel88

Original poster
Member
Dec 25, 2012
21
Just pm me ur address. U dont need to pay for postage. Im leaving for vacation in an hour or so, so i will send it when i get back.
 

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