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Tech II Not communicating with vehicle check connection

24K views 42 replies 6 participants last post by  monil622 
#1 ·
OK so I'm a body man not a Caddy mechanic. I bought an 04 CTS 3.6 automatic WRECKED in the front.
The salvage yard hooked a jumper up to it and started it for me the day I looked at it. It wouldn't idle due to the tube to the mass airflow sensor being knocked off but it ran. I trailered it home, hooked up the mass airflow sensor and tried to jump it and it wouldn't start. Key stuck in ignition/shifter stuck in park/service anti-theft light on. Came here and read all the low battery voltage posts and replaced the battery with new.

After jacking with it for HOURS, I finally got it started and it ran fine, even backed it off the trailer. Turned it off and now it's the same ole key stuck in the ignition, won't shift out of park syndrome. There are several messages on the info screen such as Service Anti-Theft, Check headlamps, coolant low, etc but some of these are to be expected since the headlights and radiator are broken.

I unhooked the battery again and unplug/replug all sort of fuses, loosen and retighten all the grounds in the engine compartment I could find and checked the harnesses externally for any damage which I found none other than the windshield washer fluid level sensor wires severed, no big deal.

Suddenly after checking the fuse boxes under the rear seat and wiggling the relays the thing starts, shifts and the key comes out. GREAT!!! I thought I had it fixed but the next day it's back to the same key stuck/stuck in park, won't start, service anti-theft mode again!!

I borrow a Tech II and hook it up. When I go to check codes it says unable to communicate with the vehicle and to check the connection and ignition on/off. I'm running the Tech II with the ignition on,duh.

I'm stumped why the Tech II will not communicate let alone why the key/shifter stuck/service anti-theft crap. Any suggestions where to start looking?
I'd greatly appreciate any help and unlike some other posters I always come back and post the solution to hopefully help others.
I can get the Tech II again if needed.

One other bit of info, It looked as though the wires to the C103 connector on the right side of the engine were pinched in between the shock tower and ECM harness. I looked this up on the GM service website and the connector has two wires, a blk/wht that goes from the battery negative to the DIM and another wire that is blunt cut somewhere in the harness according to GM. The supposed blunt cut wire looked pinched near the connector and had a single strand of wire protruding from the sheath, this wire supposedly serves no purpose, should I be concerned with it? The blk/wht wire next to it, whick serves as the ground to the DIM looked undamaged.
 
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#2 ·
To start with, do you have a CANdi module?
04 will be GMLAN and it may not communicate with lots of systems on that car without the CANdi module.
Take a DVOM and gently (so as to not damage any terminals) check from pin 6 to ground with the key on and read the voltage, it should vary somewhere in a fairly low voltage range. Then check pin 14 for the same thing.
They should have slightly different voltages but the key is to make sure they are not steady, if it is 12V then it is shorted to power and 0 would indicate a short to ground.

Next with the key off you can use an ohm meter and check from 6 to 14, you should see 120 ohms. (approximately)

If any of those readings are way off let me know.
 
#4 ·
ewill3rd Someone trashed my multimeter so I haven't been able to perform the tests you suggested.
However I did try this; I connected the Tech II, ignition on, everything I tried to read a code from showed U1000 communication error and you could clear the code such as to the Antitheft and door modules, but they would re-appear immediately. EXCEPT the ECM and trans module. Everytime I tried to read the ECM or transmission module there was no code such as U1000 it would simply say unable to communicate with the VEHICLE and to check the connection and ignition on/off.

When I remove the connections to the ECM and reconnect the battery and tech II and turn the key on I can communicate with the Transmission control module as well as the door and antitheft modules. This time I can clear the door and theft module codes and they do not re-appear even when cycling the ignition/tech II on and off, BUT the transmission module now shows error codes such as unable to communicate with ECM which is expected since it's unplugged but the trans module is now communicating.
Would this indicate the ECM is bad and causing the others to not be able to access the communication line to the Tech II?

Am I on the right track?
 
#6 ·
Re: Tech II Not communicating with vehicle check connection SOLVED!

Thanks to ewill3rd and dkozloski for thier input and as promised I am posting the solution and how I determined it.
After the latest test im my previous post I did consider what you are saying dkozloski. I was afraid that if I bought a used ECM and there was a pinched/cut wire I was back to square one and suddenly I remembered my days at Delphi Electronics making ECMs for GM vehicles and boats and we would take them straight off the assembly line and bake them before testing. If they passed this HOT test then they went into a freezer for 4 hours and were immediately COLD tested. If this test passed they were flashed and shipped.

So I got to thinking how it started outside in the cold at the junk yard and when I got it back here to the shop I pulled it inside the WARM shop and replaced the two bent inner tie rods to get the wheels straight before trying to back it off the trailer. It had plenty of time to get up to room temp and thats when the problems started.

Soooooo to rule out a bad wire somewhere I removed the ECM and put it in the freezer for about 3 hours. Once it was good and cold I reinstalled it and hooked the battery up and WAH LAH!!!! Everything is working as it should!! I hooked the Tech II up and there are no codes anywhere in any modules like there was before. EVERYTHING is communicating!

I have every reason to beileve it's a bad ECM and not a wire issue otherwise it would have the same symptoms if it were a bad wire. Sound Correct?

Thanks again to everyone for your input. Hopefully I can get a used ECM delivered this week and get it programmed.
If anyone has anything else/experiences to contribute please do so.
Whew!!!!
 
#7 ·
Having fixed many an electronic nightmare myself, my hat's off to you for your perseverence. Sometimes, that's the biggest difference between a good tech and a great tech.

One question: After you re-tested with the cold ECM and determined Life Was Good, did you re-test it again at room temp? I ask because your problem could be as simple as a connector re-seat issue. If the car still communicates and doesn't display any DTCs, I'd clean any connector(s) associated with the ECM, re-test and call it good if everything continues to pass.

CC
 
#8 ·
Good question ccclarke. I forgot to mention in my previous post that I did wait until the ECM returned to room temp and tried to start again, just as I suspected it was back to the same symptoms.

Just to disprove a wire/connection issue I froze the ECM again and will try it again on monday cold and once again wait for it to come back to room temp.

Like I said, I'm a bodytech not a full fledged mechanic and this reminds me of a tuneup I performed on a friends truck once. he had it in 3 shops and they couldn't figure out why it was running so rich, it was carb not injection.
I jacked with it and jacked with it and the more it beat me the more determined I got. I finally figured it out after 3 shops couldn't. Sucker had a small pinhole in the casting to a passage from the main jet on the bottom of the carb that was sucking extra fuel under intake vaccume.

I'll post my findings tommorow after I try another cold then warm start.
 
#9 ·
I'd have to look at the schematics for the data bus.
It sounds like a high speed LAN problem.
Traditionally they would use the ECM as a gateway for the TCM but if they tied the TCM on the bus by itself and have it set up to use GMLAN then you could be on to something.
If you had a wiring issue you'd see a lot more trouble on the high speed LAN bus.
Again you'd have to see the schematics but....

As I look at the schematics I can see that the TCM and ECM are both on the keyword 2000 bus AND the GMLAN high speed bus.
The ECM data actually comes through the TCM to the DLC (data link connector).
That COULD mean that the wires between the TCM and ECM are damaged but it would have to be an open. (shorts to power, ground, or eachother would take away TCM data)

I am not sure doing a resistance check on your GMLAN circuit would yield the results I stated earlier, I only see 2 modules on the high speed bus and there are no terminating resistors shown in the schematics as we see on most GMLAN circuits.
I would tell you to disconnect the ECM and test the continuity of the wires from the ECM to the TCM... however, those are what we call micro 64 connections and they are incredibly fragile. try not to probe those connections.

I would carefully inspect the wiring from the ECM to the TCM and be sure there is no damage and then you might go with your original assumption.
If the wires are damaged and you replace the ECM you may have programming issues with the new one.
It will need a couple of programming procedures before it will be operational.
 
#10 ·
Well I achieved the same results as the previous cold/warm (room temp.) tests. After freezing it again the thing started right up with no DTC's and 60 minutes later it was back to the same symptoms.

I would be amazed if it were anything but the ECM since the ONLY variable is the temperature of the ECM that is causing the malfunction. Everything else is a constant other than the very short amount of harness that moves during ECM installation and even then that is not disturbed when I allow it to return to room temperature.

It makes perfect sense what you stated ewill3rd as in it sounds like an open wire. I'm thinking when the ECM is frozen it contracts restoring the open connection and during expansion it becomes open once again.

I found a used ECM for $75 that should be here tommorow. Hopefully I can get it on and programmed that evening but if not I will post the results Wednesday night.

Thanks again everyone!!
 
#11 ·
OK guys, I FINALLY got this car done! It was a total loss I paid $4922 for and now I have about $7500 in it, but it is a really nice peice!!.

As suspected it was the ECM that was bad. Thanks to a doofus tech at the dealer I work at I wound up spending another $350 for a AC Delco ECM because the jack a$$ put the wrong program in the used ECM I bought.

He convinced me the used ECM was bad so I bought the AC Delco. Then he said he couldn't get the new ECM to work because the anti theft module was showing it was bad.
I told him he was nuckin futs and asked why wasn't the theft module showing that when the original ECM comes straight from the freezer?

So I made him walk me through his calibration selection process and sure as chit,,, he was selecting the wrong calibration for the ECM!! he said he didn't realize it was an LY7 engine code. Cost me $350 because they wouldn't take the AC Delco back after that.

Al I can say is at least I had the liberty to double check him rather than being a customer off the street and at his mercy, oh and the car is nice to drive now. LOL.

On an unrelated note, there was a SEVERE vibration under load during acceleration. I re-bedded the drivetrain and it was great under load but worse in park, neutral and reverse!
I discovered the transmission mount was rubbing itself. Loosened the front engine mounts and the transmission crossmember and pryed the engine foreward and crossmember backwards and retightened everything and all is well.!! Wheew, glad that's over.

thanks again guys for all your help!!
 
#14 ·
I know Ewill3rd!! I was in total disbeliefe, too shocked.
Like I said I'm actually a body tech/painter and that would be the equivalent of painting a tricoat white car with just plain 2 stage white and telling the customer, sorry we couldn't get it to match,, ummm no sir we don't need to look at option codes!!!
Geeeeeeeesh!!
 
#16 · (Edited)
i have the same problem i have the latest tech 2 with candi moudle i got 2009 cadillac cts awd when i hook up the tech 2 some time it says candi moudle no connected some time its say dlc pin 14 and 6 and some time it say it is not connnection to vechiles so i dont know what is wrong.
when i hook up other scanner simple just the code reader scanner bought from pepboys new one it just say error when readding the code so what does that tel me and i have also check the ohm on 14 and 6 on dlc i am getting 56 ohm is that right or too high what it suppose to be thanks
 
#18 ·
There has been a rash of knockoff Tech 2 and CANdi modules out there.
At any rate if you cannot establish communication check the cables and if you can, try it on another car.
Where did the Tech 2 come from?
 
#19 ·
from here in chicago his name is rick 7738604119 RJE Diagnostics i have software of 30.05 installed which cover 2011 and i have check the dlc pin 14 and 6 i am getting 56 ohm so i do not know is that right. give me a update thanks i really appreicate but the thing is i do not have other gm car so where else i can check it let me know and how to diagonistics the candi module
 
#22 ·
Did you buy this Tech 2 or are you borrowing it?
30.005 is the latest version I think.

56 Ohms is good for the GMLAN circuits, 4 and 16. That means both terminating resistors can be seen.
I'd have to look at a schematic from here.
You can't communicate with anything?
 
#24 ·
It is impossible to say what may have "burnt" the BCM up, but I would certainly be careful about replacing it.
Make sure no issues show up right away and if they do address them quickly.
 
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