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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27664
Experience:  GM Grand Master Technician 2007. 11 years experience.
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2003 chevy tahoe z71: wont start..battery keeps going dead..electrical

Resolved Question:

my 2003 chevy tahoe z71 wont start and the battery keeps going dead and when it does turn on it says unknown driver and none of my electrical will work
Submitted: 3 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 3 years ago.

GM Tech (Cam) :

Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.

GM Tech (Cam) :

How long does it take to make the battery go dead?

Customer:

um as soon as i shut it off it takes a few mins before it goes dead, when the battery is charged and i try to start it up it will sound like its abt to start but then just sputter

Customer:

and all my electrical doesnt work and it says unknown driver in the in dash thing

GM Tech (Cam) :

Ok, lets start with this, take the battery and have it tested. We need to start with a solid base, in this case battery fully charged and known to be good prior to all other testing

Customer:

ok i was at autzone a few hours before that and they said the battery is good

Customer:

and so was the alternator

Customer:

all my fuses are good but everytime i shut the car off and leave it off it dies

GM Tech (Cam) :

Is there anything installed that is not GM?

Customer:

nope everything is stock except rims and tires and that should be a problem

Customer:

shouldnt*

Customer:

ive read up online about the "unknown driver" message displayed and people say you need a new ecu

GM Tech (Cam) :

ok, then you need to do the test. CLICK HERE FOR DIRECTIONS

Customer:

and that is going to do what? ive tested all my fuses and none are blown at all

GM Tech (Cam) :

It will determine which fuse and branch the drain on the system is.

Customer:

ok, even when the battery wasnt being drained none of the electrical was working and the car wouldnt go into 4 lo and the radio wouldnt work and i mean no electrical at all and it would start and there was a message displayed in the electronic odometer saying "unknown driver"

GM Tech (Cam) :

This could mean a bad Body Control Module

Customer:

and where is that located and is there a test for that/

GM Tech (Cam) :

That is under the steering column and the testing I outlined is one part of the test. It is a computer so the testing is complicated and needs some special tools.

Customer:

hmm ok so if i replaced the body controle module should that fix the problem of the "unknown driver"

Customer:

and make my electrical work?

GM Tech (Cam) :

There is a chance yes, but without testing we cannot know and to simply replace it would be guessing at this point. That is why I posted some instructions.

Customer:

ok so for those instructions do i need any special tools or is it that basic

GM Tech (Cam) :

That you need an electrical meter that will read DC amps.

Customer:

ok, now if i do that test that will show where my power is being drained to and it will determine whether or not my body control module is good or not?

GM Tech (Cam) :

That is the idea yes. USually if you find the power drain, that will correct the other issues.

Customer:

ok so find out where the power is being drained then cut that off and see where that takes me, after that if it still displays the "unknown driver message then i need a new body control module

GM Tech (Cam) :

YEs that may be the case. don't get too far ahead.

Customer:

i wont, what im gunna do is tomorrow im going to have a family friend go through the electrical and see where the power is being drained from but i have a good idea where it is going, then im gunna see if that fixes the power drain issue

Customer:

then if the truck starts and functions ok im going to wait to monday to see if it still starts and everything goes good, if it happens to display the "unknown driver" message im going to change the body control module

GM Tech (Cam) :

If the fuse is for a module then you may need to replace the module. and it is my though that the BCM could be that module, but the test will tell.

Customer:

so is that what i should do?

GM Tech (Cam) :

See what fuse is pulling the power then get back to me.

GM Tech (Cam) :

There are far too many "what ifs" to spell them all out here.

Customer:

ok will it cost me more money or is it a one time fee?

GM Tech (Cam) :

Bookmark this page so you can easily navigate back to it, and so you know, you can reply at any time for follow up information regarding this issue, even after you accept my answer and I will reply.

Customer:

ok and how much do the body control module's usually cost and its located under the steering wheel in the dash right?

GM Tech (Cam) :

300 or so plus programming.

Customer:

ok and is there a certain place i could buy that from that i know ill be getting the right product? and where was it located in my tahoe?

GM Tech (Cam) :

That is the module under the steering column. If you as for a Body Control Module for your vehicle, any part store should be able to get you the proper one.

Customer:

ok ill be replyin to this message sometime tomorrow after noon, ill talk to you then and tell you how it went while i was finding the power drain

GM Tech (Cam) :

ok.

Customer:

thanks buddy ill talk to you tomorrow

GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27664
Experience: GM Grand Master Technician 2007. 11 years experience.
GM Tech (Cam) and 11 other Chevy Specialists are ready to help you
Customer: replied 3 years ago.

hey you there?

 

Expert:  GM Tech (Cam) replied 3 years ago.
Yes, whats up?
Customer: replied 3 years ago.
i changed the battery and the 2003 chevy tahoe z71 isnt not running any codes at all through the OBD port, i have a feeling its the BCM only because its displaying the unknown driver message still and alot of people are relating to that, what else could it be? it starts every time and runs fine, just none of me electrical works and none of my gauges work nor the radio etc... anything in mind?
Expert:  GM Tech (Cam) replied 3 years ago.
First thought now is the igntion switch. Do you have a meter?
Test at the ignition swtich.
Pop the tilt lever out and take the lower trim of the column off.

With your multimeter set to DC volts, place the red lead on the red wire. With the switch turned on, test the other leads with the black wire. Record the reading and let me know what those are. Repeat the test on the red/white wire. Let me know the resilts.
Customer: replied 3 years ago.
i do not have a meter but i did buy a new key and a can of spray air at walmart and i cleaned the key hole out and used the new key and it seems to work fine without any problems so far.....ill message you again if this doesnt work out.
Expert:  GM Tech (Cam) replied 3 years ago.
ok
Customer: replied 3 years ago.
what about a message saying SERVICE 4WD? any clues how to fix that?
Expert:  GM Tech (Cam) replied 3 years ago.
Replace the encode sensor in the shifter of the transfer case.
Customer: replied 3 years ago.
ok my truck starts everytime no problem. it wont allow me to use electrical what so ever and it displays the message "unkown driver" and "service 4wd" and none of my gauges read except my speedomoter and rpms. im taking it to the dealership next thursday, any ideas on what it wrong?
Expert:  GM Tech (Cam) replied 3 years ago.
SOmething causing the communications to fail.
Customer: replied 3 years ago.
are there anythings i can try before i pay like 1000 bucks to get it fixed?
Expert:  GM Tech (Cam) replied 3 years ago.
check the grounds under the drivers door on the frame.
Customer: replied 3 years ago.
after i check that and make sure its ok is there anywhere else?
Expert:  GM Tech (Cam) replied 3 years ago.
that is the main one, otherwise check the data line.
Check the purple wire at the data plug for power.

Customer: replied 3 years ago.
if i take it to the dealership and tell them exactly what is wrong with it will they be able to fix it back to what it once was, and im taking it to a chevy dealership. Everyone keeps telling me its the ECU or the BCM, how do i tell which one and how to i get those messages to stop coming up.
Expert:  GM Tech (Cam) replied 3 years ago.
ECU is what most call the BCM, as it is Electronic Control unit where as saying Body Control Module.
yes they will trace it down to exactly what is wrong and should be able to fix it.
Customer: replied 3 years ago.
i thought the ECU was located under my steering column and the BCM in under the drivers seat?
Expert:  GM Tech (Cam) replied 3 years ago.
The BCM is under the column and the memory seat module is under the seat.
Customer: replied 3 years ago.
now the memory seat module cant affect all these things right? it has to be the ECU/BCM?
Expert:  GM Tech (Cam) replied 3 years ago.
If there is a data line shorted under theseat it can.
Customer: replied 3 years ago.

how do i check to see if there is a shortage? is there a cheap tool i can buy that will allow me to check those things easily?

 

Expert:  GM Tech (Cam) replied 3 years ago.
do you have a meter?
Customer: replied 3 years ago.
no i do not, how much are they and can i pick them up from autozone?
Expert:  GM Tech (Cam) replied 3 years ago.
I think walmart has simple volt meters for 15 or so.
We want to test the purple wire to the data plug for dc volts.
Customer: replied 3 years ago.
ok autozone has 12volt ones for like 14 bucks, im gunna buy one right now, where is the wire located exactly, im not really good at this kinda stuff but im gunna try
Expert:  GM Tech (Cam) replied 3 years ago.
The port that you plug the scan tool into? On that, top row, second from the left, test form there to a ground.
Customer: replied 3 years ago.
so just run it down the wire? how will i know if its bad or not? where will the ground be that im testing it too?
Expert:  GM Tech (Cam) replied 3 years ago.
You are testing from that wire to ground. You want to see what the voltage is on that wire
Customer: replied 3 years ago.
ok well my cars auto theft protection light stays on no matter what it starts up and runs fine, the purple wire is the only purple wire under my dash right? is the ground under my car or under the hood bcuz i seen one uner my hood that goes into my car, if none of this works im gunna have the dealership replace the ECU/BCM and they said it will cost 500 including labor....
Expert:  GM Tech (Cam) replied 3 years ago.
No that will be the only purple wire in that plug and any metal inside the truck is a ground location
Customer: replied 3 years ago.
ok well i just started it up and it seemed fine for about ten seconds then my radio went out and all my gauges were soon to follow then is displayed the message service 4wd followed by unknown driver?
Expert:  GM Tech (Cam) replied 3 years ago.
I think we may need a scan tool, like one the shops have.
Customer: replied 3 years ago.

to scan what the OBD? bcuz i did and all that came up was my bad o2 sensors and i got them fixed

Expert:  GM Tech (Cam) replied 3 years ago.
that is a code reader, we need full scan tool to see wich igntion feeds or modules loose communications.
Customer: replied 3 years ago.
ok so if the shop runs the full scan tool it will for sure 100% tell them what the problem is?
Expert:  GM Tech (Cam) replied 3 years ago.
If the technician does his job and diagnoses this correctly then yes.
Customer: replied 3 years ago.
well i guess this thursday its going into the shop, how do i correctly ask for the scan so they dont just scan the obd again, have you ever heard of this problem before?
Expert:  GM Tech (Cam) replied 3 years ago.
I have heard of many issues, simply explain to them what this is doing.
Customer: replied 3 years ago.
ok well lets hope its just the ecu and its a one and done deal....im just gunna tell them to check all the wiring and grounds and replace the ECU and if they do all that correctly it should eliminate this problem, what about the service 4wd? i have to replace the sensor in the transfer case right?
Expert:  GM Tech (Cam) replied 3 years ago.
Check the issue first then when done, if the service 4wd does stay on, then it is the sensor.
Customer: replied 3 years ago.
ok well wish me luck this thursday will tell all i guess, thanks for the help killa cam

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