SOLVED! 2002 Envoy 4wd SLE with weird intermittent electrical issues

[Street]

Hi Everyone,
My first post to the forum and it's a whopper.

First, background info:
My dad acquired the Envoy (lets call her Goldilocks - cause she's a picky b*tch) for me about a year and a half ago. Goldi has 156k miles on her today. She's had a rebuilt transmission (jasper), the motor has been gone over, compression it great, and my last tank of fuel ran 17MPG. She has a bit of an odd assortment of options. The typical SLE, but add On-Star, auto-headlights, dimming mirror w/temp&compass. I'm still stumped as how the auto-headlights are supposed to work, the headlight switch is just a three position (off-park-headlights). But that one I'll save for another day.

Here is the main malfunction: At any given startup the TCCM might not wake up (no light on 4wd switch, and Service 4wd on dash); sometimes powering down and restarting "cures" it, but sometimes not. But always will comeback after few ignition cycles. But wait, not the real annoying issue.

The real one comes up as follows:
I'm cruising on the freeway, cruise on 70, window open. I decide I've had enough of the buffeting, and I'll run the A/C. Reach down and turn (manual hvac) fan from off to 3; cruise dies, and I'm coasting. First time it did this I thought I blew a fuse and was going to end up on the side of the road, then after laughing at myself for a moment, realizing the motor is still running, put my foot back on throttle, and keep moving. What I realize then is that my dash is alight! ABS, Brake, and Service4wd are all on, and no HVAC to boot; the A/C compressor is cycling, indicator is lit on a/c button, but the blower motor has no power. Turning fan on/off makes no changes; except off, turns off a/c button and compressor stops engaging.

So, I check the fuses - none are blown. And to boot, a restart and voila, HVAC fan is on and ABS/Brake MILs are off. Service4wd is still on, but I'm used that and sure enough an ignition cycle later, that's off too.

Thus, I figure I have a ground issue. I spent last Saturday with cleaning every ground point (though, they all visually appeared clean). I hit the contact surfaces with a scuff pad and got pretty shiny metal on the mating surfaces - both in the body and under the hood/frame. (I work from home, so I don't drive everyday, so she sits for 24,48,72 hrs at a time). So I'm out Friday, and Goldilocks gets me again. This time on startup, a few moments after engine is running, ABS, Brake, and Srv4wd all appear. Indicator on 4wd selector switch is lit (usually when the module doesn't wake up, no indicator lights on the switch). Cruise worked, but not the blower fan.

One last thing, I have an ongoing issue with parasitic battery drain with the factory passenger side door module. I've been through 2 replacements that work for a period of time (say a month or two) then just refuse to work (no window, no lock, no mirror.), but don't drain the battery. BUT, reinstalling the factory module gets my window and locks in the door working and it might even been good for a day or two before the drain starts again. At which point, I just unplug the connectors from the module and call it good for now -- which is the state it is in when the above happens, disconnected.

So if anyone has experience resolving these issues, please let me know. I'm at wits end with Goldilocks' issues, but I really need her to be good for another year.

 

[gmcman]

Welcome to the forum!

I'm sure others will chime in as well, but in your case, I would start with the ignition switch.

Doesn't mean that's your issue, but they have a proven record of causing a myriad of issues when going bad. They are inexpensive and easy to change.

As far as your HVAC issue, not sure. There was a thread on the cruise ccontrol a while back and I have to find it.

Your headlights do have 3 positions, I have always left it in the "O" position which is auto. There is a small, domed sensor on the center of the dash which controls the headlights, has proven a reliable feature.

 

[Street]

The headlight switch is just strange to me - every other vehicle I've seen with automatic headlights has an "A" position, usually counter-clockwise from the off - parking - headlights positions.

And I'll add checking for voltage drop across the ignition switch to my checklist. Funny, I was just watching the fella with "Minty Green" Trailblazer working on that very switch.

 

[Mooseman]

From what I can tell, the headlight switches in the US vehicles had the OFF position for the headlights however Canadian trucks don't because of our DRL laws. Maybe the switch was replaced or it's originally a Canadian truck?

The ignition switch is a good starting point, cheap and easy to replace. Next would be the ground points. There is the main one just to the right front of center console. There are others but this post will get you the others.
Electrical Ground locations

For the parasitic draw, it might not be the DDM however looks like it's related. You would have to do a parasitic draw test to find which circuit is drawing the power. It could be another module or a circuit keeping the DDM awake. Lots of info out there on how to do this test. Another possibility is a bad module that's putting garbage onto the network and cutting out all modules. You would need either an oscilloscope to view the network traffic or an advanced scanner like a Tech 2 or Snap On to check each module to find out what each one is doing or are responding. This type of problem has been seen before where a bad module brings down all the others.

 

[TJBaker57]

This might work for disabling the DRL for the current ignition cycle. Press the dome light button 4 times in no more than three seconds. There should then be a beep sound and the DRL lighting is disabled for that ignition cycle. This is how it is on the 2002 TrailBlazer. I think it is this way ONLY for the 2002 models.

 

[TJBaker57]

Here is the main malfunction: At any given startup the TCCM might not wake up

There was a TSB for exactly this on the 2002 models I believe. Failure of the TCCM to wake up. This could be your issue with the TCCM. It is unlikely to be related to the ignition switch as the TCCM gets no power through the ignition switch, it is powered all the time, even with the key removed.

Do you have one of those bluetooth OBD2 adapters? If yes I can tell you how to check the part number of the TCCM without having to remove it. I have seen a lot of 2002 models where the original was already replaced.

 

[Street]

I do indeed have a BT ODB2 adapter. I know I have had to change the TCCM, the encoder/motors on the XferCase, and the switch. The motors were frozen, the module wouldn't communicate, and well, the switch came along for the ride.

@Mooseman
I'm also concerned that a noisy bus is causing modules not to sleep when they're supposed to. I just can't catch anybody in the act.

And I did check voltage readings on Ignition 0 at the BCM(under rear seat) as compared to battery.
Battery: 14.6 volts (all tests with engine running)
BCM (Hot lead) 14.4V
BCM (Ignition 0, 10A fuse) 13.6 volts.
To me, that a drop of 1V from battery to this point is a lot, but no manual has a spec on what I should expect. Thoughts?

 

[Mooseman]

I would suspect the ignition switch being wonky. It's not a big drop but maybe a bad contact would cause it. And as more stuff draws on it, it gets worse.

 

[Mektek]

From what I can tell, the headlight switches in the US vehicles had the OFF position for the headlights however Canadian trucks don't because of our DRL laws.

Nope. US 02 TB has drl without an OFF. 4 hits to the interior light button turns headlights off.

 

[Street]

So, I know it's been a real long time since my original post; insert work excuses (though true). Still I wanted to bring some closure to the thread.

I did indeed replace the ignition switch module ($14 on RockAuto), and took about 15min to install it (14 of that was just getting the trim pieces out of the way and back in place). Two good things can from it, first, the detents for each position are much "stronger" (as in you can actually feel them by turning the key - the old one was very 'indistinct'), and more importantly, no more weird issues with HVAC, ABS, Cruise, etc.

And I measured the IGN0 bus, it's back to 13.8V (only .4V lower then right at the battery).

Special thanks to the GMNation crew, and those who commented here.