[FIXED] 2011 Chevy Express 2500 6.0L No Communication

Hi Paul,

Just reposting here for the issue that im having. Any and all help would be appreciated this thing has been stumping me for 2 days now and everything i have tried has gotten me no further to the cause of the issue. I am getting coms on the serial network but nothing on the CAN network.

Can you post us a wiring diagram? Also have you checked pins 6 and 14 for 60 ohms at the data link connector. I’m not sure if it uses a gateway module or not. If it does then that test is invalid

If it were a guess I’d say ebcm or airbag module seems like those 2 always are issues

I can and will post a diagram tomorrow. What i didnt know is that the customer tried to work on this vehicle themselves and there are wires that have been cut. I now have to go through and verify that things are going where they should as it looks like they may have tried to bypass something. This is going to a huge headache but im bound and determined to figure this out. I do know if i unplug the BCM i lose all communication period without jumping the communication wires at the BCM connector. Have tried that still did not restore communication to anything. This thing really has me puzzled but there is a language barrier with the customer and im not sure what they did before it came to us which makes things alot harder at this point. I have so many diagrams printed at this point to try to find where my culprit is because at this point im sure they cut or got into a wire they shouldnt have and that is now the main focus trying to find what cut wires i can find and where they belong. Thanks ahead of time for all help and suggestions I will need all the help i can get with this one.

To be clear, you have no communication on high speed GMLAN, but have communication on the low speed GMLAN? Does this van start and run, or is it a no crank?

Cheryl is right on about doing some quick checks at pins 6 and 14 of the DLC. I'd like to see:

1.) Resistance across both pins with the key off.
2.) Voltage between pin 16 and pin 4/5.
3.) Voltage between pin 6 and 4/5 with the key on.
4.) Voltage between pin 14 and 4/5 with the key on.

Yes i have no communication on the high speed but have comms on the low side will get pictures of the things you requested as soon as I can.

Tourres wrote:

Yes i have no communication on the high speed but have comms on the low side will get pictures of the things you requested as soon as I can.

Love it. Thank you!

I also need to clarify, you have no communication with ANY module on the high speed GMLAN? Or only select modules?

15.7K ohms across 6 and 14 is way too high. That may also explain why the voltage is too high on CAN High pin 6. Would you be able to take this reading again? Key off, open and shut the drivers door and wait a minute. I'm sorry to ask you to redo this, I just want to make darn sure.

If the high resistance remains, we'll want to break the network in two and test resistance in both directions. You said you have access to the BCM? We can use that as a testing point if the connectors are easy to get to.

yes i have no comms to any high speed module. That reading was taken first thing this morning before anything was turned on and with the door latch tripped so that i could get to everything. I can access the BCM very easily as i have already been there for testing. I have tried disconnecting the high speed lines at the BCM and jumpering them as i found a different forum that suggested that to see if i could get comms back to the ECM. My signals did seem to clear up a bit when i did that but still had no comms to the ECM. this things has been a nightmare for the last 2 days and am about at my wits end with it lol.

Tourres wrote:

yes i have no comms to any high speed module.

Gotcha, thank you.

That reading was taken first thing this morning before anything was turned on and with the door latch tripped so that i could get to everything.

Excellent.

I can access the BCM very easily as i have already been there for testing.

Awesome, we'll use that. Key off and out, cycle the door and latch it. Disconnect X3 (light blue). One resistance measurement between 8 and 9. Another between 16 and 17. That'll point us either towards the ECM, or towards the transmission/TCM.

I'm guessing we're gonna end up at X100 or X101 before we're done. :silly: But this'll work for now.

this things has been a nightmare for the last 2 days and am about at my wits end with it lol.

Don't yeet this one into the lake just yet. :lol:

Ok so here are my readings from the X3 connector at the BCM. The connector was disconnected of course.

Tourres wrote:

Ok so here are my readings from the X3 connector at the BCM. The connector was disconnected of course.

No offense, but are you sure the ohm meter in your Verus is working correctly? Do you have another meter handy? Again, I'm not questioning you, just making sure.

If those readings check out, we have at least two problems. :silly: A open circuit between the BCM and the ECM, and excessive resistance towards the EBCM.

My preference would be to go for the open circuit first. Fewer variables, easier access. As I said earlier, I believe X100 or X101 is gonna be the next best bet. Let me know which one is easier to get ahold of, and we can restest.

It seems to be working correctly and I calibrate before every test and it seems fine with calibration before testing i do have another meter but its not one i trust very well. The X101 seems to be the easier of the 2 to get ahold of or i could back to the EBCM as its very open and easy to get to as well from underneath the van. I will try some measurements with my other meter just to be safe but everything seems to be right on the verus.

I retested with my other meter still got an open on one side and 49 kOhms on the other.

Tourres wrote:

I retested with my other meter still got an open on one side and 49 kOhms on the other.

I appreciate the recheck. Didn't want to send you down the wrong path.

X100 would be the way to go to track the open, IMO. Reconnect X3 at the BCM, then disconnect X100 and measure resistance across pins 36 and 40 in both directions.

I will give this a shot and get back to you when I have completed the test. Thanks for all your help thus far.

Here are the readings that i got from the X101 connector. The male side appears to be about spot on at 120ohms if the way im thinking is correct because one of the resistors in the circuit is not in play. The female side still shows very high resistance. My problem is im not sure which side goes where to be honest?

Ok so update, while I was unplugging the X100 connector I saw that one side of the connector latch was not seated properly. After testing i went to put the connector back together and made sure everything was latched the right way. At the same time I had the labscope hooked up to the DLC just to see what signal I was getting and the signal didnt look terrible while the connector was unplugged. After seating the connector the right way I got full communication signal back. The vehicle then started and all the resistance test came out spot on. I guess lesson learned check connections!!!! Thank all of you especially Tyler for all your help while i was dealing with this issue. It was much appreciated!!!!!

Tourres wrote:

After seating the connector the right way I got full communication signal back. The vehicle then started and all the resistance test came out spot on. I guess lesson learned check connections!!!! Thank all of you especially Tyler for all your help while i was dealing with this issue. It was much appreciated!!!!!

:woohoo: That's what I like to hear! It's never easy when someone has been monkeying around before you, doing God-knows-what in the wiring, AND there's a language barrier.

Now that it's up and running, do you think X100 being loose was the original problem? Or just an installed problem?

Speaking of X100, I wanted to revisit something I said earlier:

If those readings check out, we have at least two problems. :silly:

Well, those readings did check out. But we DIDN'T have two problems. Really, (I think) it was two problems at one connector:



Does this make sense? Or did I miss something else?