Unknown driver, warning lights, not quite like this issue in other forums

[bmonkey]

Okay everyone, I’ve exhausted the forums searching for a solid diagnosis for this. Nothing hits right. I have guesses, but don’t want to start throwing expensive parts at it. Any help before going to the repair shop would be most appreciated, especially since I’m not convinced a shop can figure this one out on the first or second attempt.

2004 GMC Envoy XL, SLT, 4x4, V8, 108k miles, no aftermarket electrical or engine mods.

The first symptoms are fairly common to other forums:

“Unknown Driver”

Things that don’t work:
Lock/Unlock on FOB and front (driver & passenger.) door buttons.
Windows from front (driver & passenger) buttons. Rear windows do work from their buttons.
4WD
Stereo
Diagnostic link – has power to light up Bluetooth style ODB 2 reader, will not connect to phone as before, ODB 2 reader works fine on other vehicles

Things that do work:
Power mirrors
Blower / Climate Control
rearview mirror buttons
Sunroof
3rd row windows
Rear heat & a/c
Headlights (including high beams)
Driving lights
Turn signals
Headlight washer fluid (relay for this currently pulled because goddamn I get sick of being sprayed every time I reconnect the battery!)
Shifts normally

ABS, Parking Brake, Airbag, Battery lights on. Check Gauges, Service 4WD, Low Fuel lights WERE also on (see below for update). Tach works, speedometer presumably works, no other gauges work.

No blown fuses (tested and inspected) or bad relays (tested for operation and continuity) under hood or under rear seat.

Battery tests as good at 2 shops plus home charger

Alternator tests good with multimeter (14v+ when running)

Checked rear hatch area for possible short as mentioned in other forums. All is fine.

Inspected as many grounds as possible. All were fine. No rust, corrosion, etc.

Pulled bus bar from splice packs (SP205 & SP305) – no change except Check Guages and Low Fuel lights are added if front SP bus bar is pulled when running. I assume this rules out bad modules.

When problem first started disconnecting battery for 12+ hours and charging, then reconnecting would restore all functions, however this would only correct for 5-10 minutes, running or not.

Presently disconnecting battery and charging has no affect. Same symptoms upon reconnecting battery.

Ignition switch replaced, knowing it was almost certainly fine. Did not fix the problem.

When replacing ignition switch I removed instrument cluster to have a look. While moving the cluster all function returned depending on how it was moved, turned, etc. I cleaned all contact points on back of circuit board. I haven’t pulled it totally apart just yet for fear of damaging needles. It is still not working. HOWEVER, the Check Gauges, Service 4WD and low fuel light are no longer lit. Moving the cluster around, tapping it, wiggling the connector no longer has any affect since cleaning it.

Before messing with instrument cluster and replacing ignition switch (not sure which had the affect), if “unknown driver” was displayed engine would turn over and run for 1-2 seconds, but immediately die. Now the engine will run fine with “unknown driver.”

Battery drain with IC connected AND disconnected (dead within 12 hours). Since the battery is also draining with the cluster disconnected I’m not convinced that’s the problem.

What else? Do not have DVD player (read about wiring issue on that somewhere). Once or twice when charging battery with everything connected charger indicated “bad battery”. This is not usual and does not happen if battery is disconnected, no doubt because of draw.

What else should I be checking? What would you all try next? Thanks!

 

[Mooseman]

Have you checked the threads on this site for Unknown Driver?
https://www.google.ca/search?site=&...5i39k1j0i131k1j0i22i30k1j33i160k1.GgxaE5k0_2U

Most seem to point to a defective module somewhere throwing gibberish into the data bus.

 

[AtlWrk]

The next step is to remove the fuse(s) from each module on the data bus one by one until you find the culprit. The most likely culprits IMO are the instrument panel (IPC), driver's door module (DDM), passenger door module (PDM), OnStar computer (VCIM), and brake module (EBCM). Several of the modules have multiple power supplies so it may be more thorough (but a bit more work) to actually disconnect their connectors to be absolutely sure they're off the bus.

Removing the splice packs just isolates everything from everything else which has the same effect as a bad module corrupting the databus: no one can talk to anyone. This is also why your battery is draining--when the ignition is turned off the BCM and/or PCM sends out a message telling all the other modules they can go to sleep. Without this message some will stay active sucking up significant power (OnStar is notorious for this failure mode). This also means just hunting for a current draw may lead you to falsely accuse modules who just don't know better.

If the fuse route doesn't bear fruit than you may be looking at a wiring issue (e.g. a short) on the databus.

 

[Tiggerr]

IIRC isn't it the module in the liftgate that deals with the keyless entry and all that?....
Could be that module, or that harnesss in the boot of the liftgate at the top shorting something out...
I know that harness is prone to that...

 

[bmonkey]

Thank you all for your ideas. I've read what feels like 50 threads on the subject. My focus was on the easy things to check first. Now it's time to get dirty.
After replacing a blown fuse on my multimeter last night I ran another test for parasitic drain (leads on negative battery post and cable) and came up with a roughly 3 amp draw. That number was moving all over the place, so it's an average. Pulling fuses and relays in from the box under the hood did not result in anything significant. The average stayed the same. I had a bit more luck with the box under the rear seat. Pulling fuse 41 for the radio dropped the draw by 1.4 to 1.5 amps. Nothing else there had an effect. Removing the bus bar from the rear splice pack dropped that by another 1 amp. That got me down to a range of 0.3 to 0.53. That doesn't tell me much, but it's a lead.
I've checked the wiring going through the boot in the liftgate with no results, but I still haven't ruled it out simply because it seems to be such a common problem. I plan on pulling the inside panel and tracing the wiring through the harness to make sure.
Good idea on the Onstar computer. Removing it can't hurt, and I might as well since it's no good to me.
Again, thanks. This is all very frustrating - having knowledgeable people helps.

 

[AtlWrk]

Another idea:
Pull the bus bar from the front splice pack then use a small wire to jumper positions A and B (the purple and dark green wires, respectively). You should now be able to connect your Bluetooth adapter to the PCM (ignition on) and get something like engine coolant temp data. Next, add a jumper between the one you already did and the next position so three positions (A, B and C) are connected together and verify your adapter is still connected to the PCM. Then do A, B and D, etc. and work your way down until you find one that prevents your adapter from connecting to the PCM--this will be your problem module.

If you don't find anything here, reconnect the front bus bar and disconnect the rear one. Jumper position M (dark blue/white stripe) to each of the others one at a time (only two terminals connected this time).

Hopefully doing this will find one that is crashing the databus.

 

[bmonkey]

Excellent idea and definitely not something I would have known to try. I'll try this after work tonight.
I should have noted that removing the bus bar from the front splice pack had no affect on my readings last night. I don't know how significant that is. A bad module (one of the ones you pointed to) makes sense at this point.
Would you agree that it's probably not the instrument cluster since the issue is there whether it's plugged in or not? The fact that the issue went away momentarily when I rattled the thing a bit doesn't make sense though. Like I said, rattling has no affect anymore.
Thanks!

 

[AtlWrk]

I should have noted that removing the bus bar from the front splice pack had no affect on my readings last night. I don't know how significant that is.

This is what I was getting at in post 3 when I said:
"Removing the splice packs just isolates everything from everything else which has the same effect as a bad module corrupting the databus: no one can talk to anyone....This also means just hunting for a current draw may lead you to falsely accuse modules who just don't know better."

A bad module (one of the ones you pointed to) makes sense at this point.
Would you agree that it's probably not the instrument cluster since the issue is there whether it's plugged in or not? The fact that the issue went away momentarily when I rattled the thing a bit doesn't make sense though. Like I said, rattling has no affect anymore.
Thanks!

Without having seen the behavior myself I'm not ready to rule it out though it does seem unlikely now.

Other question: Any other work been done on the truck recently? Anything that could have disturbed wiring harness?

Also, you can start and run the truck now--just no databus dependent functions (like what you listed in the first post), correct?

EDIT: Also, please tell me you took out your Bluetooth adapter at some point to rule out a faulty adapter? (Actually just saw you tried it in other vehicles, nvm).

 

[bmonkey]

Still figuring out how to reply with quotes.

Regarding any work I've done, about 2 weeks prior I replaced the water pump and the radiator (bumped it enough to put a hole it it while removing the pump - doh!). I cleaned the engine with some degreaser, but focused on the block itself and was careful not to get water on the alternator, battery, PCM, etc. Nothing else that would have disturbed a harness other than trying to track down the issue now (removing panels, etc.).

Correct, it now starts and runs great. I just have the ABS, Parking Brake, Airbag and battery lights on, plus no gauges other than tach and speed. Radio, front window switches, power locks and 4wd are out. All else works (when the battery is not dead).

And yes, I used the Bluetooth OBD2 on another vehicle to chase down a misfire. It's worked in the Envoy many times and still works in both of my other vehicles.

Thanks!

 

[Mooseman]

To reply to a particular post, just hit the "reply" button at the bottom right of the post. If you just want to reply to a portion of a post, highlight what you want to quote and an option to "reply" or "+ quote" will appear. Reply will put it right away into the reply. + quote will add it to multi-quote and then you have to use the "insert quotes". Reply works much easier IMHO.

 

[budwich]

some of the draws are related to things not yet "sleeping" so you may not be able to totally rule them out until they "sleep". IIRC, the main issue is likely the liftgate module... try unplugging it. It may be "bus chattering" causing issues but also some of its "chattering" might be "squawking" resulting in the radio being left in a "warning state / turned on" causing a high drain there... plus other issues with the bus itself.

 

[bmonkey]

A quick update - with the bus bar from the front splice back out I ran a jumper from A to B. Nothing. I added C and still could not get a connection to the ECU. The OBD2 unit has power and the "connecting" light flashes, but won't connect. I also jumped A,B & D, A, B & E, and so on without success. I'll chance driving it to the parts store tonight or tomorrow and see if they can read anything.

I also disconnected the following modules without success:
Onstar unit, EBCM, LGM, DDM, PDM.
I will note that when I did a draw test with all of these units disconnected (plus IC unhooked and radio fuse out) I got a draw of 10 mA. I started reconnecting modules to see when the spike occured. It didn't. With everything reconnected the total draw ended up being 30 mA - acceptable I believe. Feeling confident that cleaning a few grounds that looked perfectly fine indeed fixed the problem I reconnected the negative battery terminal. Same issues remain and another draw test shows the system is still pulling about 2.9 amps.
Just one thought that I had - when I reconnected all of the modules I failed to actually reconnect the harness for the liftgate components where it passes through the body. I'll have to do that tonight. Not that it would explain the draw that still exists...

 

[Mooseman]

When checking the draws, do you wait to see if modules and such go back to sleep? Even something as simple as opening and closing a door will wake a bunch of things up for a while. I remember on my EXT that when I opened the door, the fan for the interior temp sensor would turn on, which would mean the HVAC module would turn on. Then there's also RAP that keeps almost everything on for 10 minutes.

 

[AtlWrk]

A quick update - with the bus bar from the front splice back out I ran a jumper from A to B. Nothing.

This alone is very telling. You only need power, ground, and a data connection between the PCM and OBD adapter (jumping A to B) to establish communication. Assuming you had the ignition on (correct?), not being able to connect to the PCM this way indicates there's an issue around the PCM itself since all other modules are out of the equation.

You mentioned degreasing the block. Have you since inspected and cleaned the grounds on the block? There are a few (3 on the 4.2L, not sure about the 5.3L) on the driver's side and one of them is G108: the one and only ground for the PCM. It's low on the block, near the front, right above the front differential. It's a bit awkward to get to but a critical check at this point.

If that doesn't work, pull the front bus bar again and jump M (light green) to H (dark blue with white stripe)--this reconnects the door modules to the BCM. See if you can control the rear door locks with the front door switches. If you reconnect the liftgate harness you should also get your remote locks back with M and H jumped.

Alternatively, you pull the PCMs fuses since that's what we're trying to get at the moment: to see if we can get some modules talking to each other without the PCM on the line.

I know it's been a ton of fussing. We will figure it out...

 

[bmonkey]

When checking the draws, do you wait to see if modules and such go back to sleep? Even something as simple as opening and closing a door will wake a bunch of things up for a while. I remember on my EXT that when I opened the door, the fan for the interior temp sensor would turn on, which would mean the HVAC module would turn on. Then there's also RAP that keeps almost everything on for 10 minutes.

I would guess everything went back to sleep. With everything except the hood closed I've let it sit for 30 minutes or more and checked the draw again. I suppose it's possible that when I turned my multi-meter back it it woke something up?? I could try leaving the meter on.

Assuming you had the ignition on (correct?), not being able to connect to the PCM this way indicates there's an issue around the PCM itself since all other modules are out of the equation.

Definitely had the ignition on (although the reader power and comm lights flash with it off too). I meant to check my other vehicles to see if that's normal.

I know it's been a ton of fussing. We will figure it out...

You're awesome. All of you that are helping to figure this out, it's greatly appreciated and I'll figure out how to repay it.
I'll report back tomorrow.

Mod Edit: Please use the +Quote button instead of posting consecutively to reply to each post. Thanks.

 

[bmonkey]

Okay, I checked what I believe was the ground for the PCM - low on the block right above the front diff just as described. I did just look up some diagrams and now I'm not totally sure that wasn't G107, so I guess I need to double check. Regardless, that connection was clean and solid.
Jumping M to H on the splice pack didn't do anything for me.
The last thing I did was pull fuse 10 for PCM B. With M and H still jumped I got the door locks. I reconnected the bus bar and got everything back online except the 4wd selector. The only light on the dash was "service 4wd" plus "check gauges." Driver 1 and 2 were recognized, windows, locks, key fob, etc. are all working. Obviously the engine will not turn over. Removing fuse 28 for PCMI takes down everything else.
With fuses 10 and 28 out I still have a draw of 3.5 amps after 30 minutes and after 11 hours.

 

[Mooseman]

Well, seems like the PCM is causing the unknown driver and other issues. I'd put all the fuses back and disconnect the PCM. Does the '04 V8 PCM have a separate TCM (Transmission Control Module)? If so try it too as the naming in the fuse box may be PCM as well.

 

[bmonkey]

Question: do you think this kind of corrosion and... let's call it "mud" on the connection point to PCM would cause the electrical issues I'm experiencing? The answer seems to be "absolutely." It appears that water was somehow running down the wires and making its way into the plug. I clean all of this up, reconnected and I think all of my problems are solved. Everything that was screwy is corrected and all functionality seems to be back to everything I observed and tested. I did notice that I have still have a draw of 3.5 amps which is quite high, checked about 30 minutes after disconnecting the battery. I'm not entirely sure actually disconnecting the battery doesn't cause that though. The battery was at 12.75 volts last night and 12.58 this morning, about 10 hours later. A minor drain, but nothing like a constant 3.5 amp draw would cause. Typically the battery would be down to 6 volts if not totally dead if I left the negative terminal connected overnight. I'll follow up in a few days, but I think we can call this one solved.
Thanks to everyone for helping me figure out what to check and do. You're all awesome. I'll try to help out others in the future and will definitely be making a donation to the site.
Thanks!!

 

[AtlWrk]

Glad you figured it out!

Usually the PCMs are relatively bulletproof so they're low on the list of possible root causes. Chalk one up to systematic process of elimination

 

[mrrsm]

Just a "late to the party" suggestion on two other possible problem places to consider adding to the good, systematic checklist you followed:

(1) Cabin Overhead "Vanity Light" switches being stuck half way between the On-Off positions.

(2) Jammed or Broken Door Jamb Interior Light Kill Switches.

 

[JohnW]

Question: do you think this kind of corrosion and... let's call it "mud" on the connection point to PCM would cause the electrical issues I'm experiencing? The answer seems to be "absolutely." It appears that water was somehow running down the wires and making its way into the plug. I clean all of this up, reconnected and I think all of my problems are solved. Everything that was screwy is corrected and all functionality seems to be back to everything I observed and tested. I did notice that I have still have a draw of 3.5 amps which is quite high, checked about 30 minutes after disconnecting the battery. I'm not entirely sure actually disconnecting the battery doesn't cause that though. The battery was at 12.75 volts last night and 12.58 this morning, about 10 hours later. A minor drain, but nothing like a constant 3.5 amp draw would cause. Typically the battery would be down to 6 volts if not totally dead if I left the negative terminal connected overnight. I'll follow up in a few days, but I think we can call this one solved.
Thanks to everyone for helping me figure out what to check and do. You're all awesome. I'll try to help out others in the future and will definitely be making a donation to the site.
Thanks!!

BMonkey you and I have almost the identical problem. Mine went out last Sunday during a heavy thunderstorm and I titled my thread 'struck by lightning?' I did not know what to search for when I had such a long laundry list of problems. Go read my post, we have almost exactly the same dead electrical items.
When I read your posts about the dead battery/current draw when shut off, my heart sank. I bought the most expensive battery Ive ever bought about 6 months ago and if it was sucked down to completely dead....well they are never the same after that.
I have had no time to work on it and have not started it since we got home 5 days ago. I was expecting a dead battery, but when I slowly turned the ignition key on, I was shocked to hear the radio. And guess what...everything is now working. That sucks, hard to fix anything that is intermittent. Since it was raining hard when this happened, maybe I have the same problem you had. I will certainly look at the PCM connector tomorrow.

Mod Edit: Posts merged. If you wish to reply to a post, hit the Reply button in the post and then start typing below the quoted post. Thanks.

 

[bmonkey]

Since it was raining hard when this happened, maybe I have the same problem you had. I will certainly look at the PCM connector tomorrow.

It's certainly possible. In my case I suspect the water was getting in from under the hood while driving. It also may have happened when I was cleaning the engine - I stayed away from the PCM with the water, but it could have followed those wires from some distance away. I'd also check the harness going to the rear liftgate where it passes through the body that many have suggested if you haven't already. The seal above the hatch isn't great on mine (XL) and I get some water dripping through in the carwash and heavy rain. Maybe it's not an issue with the short body. At any rate, when I checked my wiring in this location as part of the troubleshooting I did find one wire that had cracked sheathing. The wire was fine and wasn't touching any other wire or metal, but if water got in there I could picture it shorting on the body.