Hey everyone been rebuilding my abounded c6. Came across ABS Problem.

Had the dreaded ABS C0121 valve Relay circuit. Decided to get another EBCM unit.

resolved the issue. However, I got a different code after installing my used own
U2107 Lost communication with BCM

So I decided to exchange the Ebcm at the salvage yard for another thinking it was the problem.

however different EBCM again, and same code U2107

i checked all the grounds. All BCM/EC. Connectors. Harness.

whats weird though.

when the car is key switched on, my tech 2 says it passed and the code is no longer there. As soon as I turn the vehicle on/run the code comes back U2107.

so my bcm glan sees it and passes during accessory/switched which leads me to believe it’s something else and I honestly don’t know what it can be I’m at a loss. I both the alldata and tech manuals and nothing in there about resolving this.

Another weird symptom after installing the used EBCMs. The car will run for a bit, and then just shutoff. It won’t do it all the time, but my old Ebcm never did this even thought it was faulty.

Do I need the dealer to program the used EBCM?? I thought used EBCM didn’t need to be programmed? Especially since the code goes away/passes when the ignition is switched on.

ready to resolve this so I can move on to other little issues


any help I’d appreciated!

Ignition switched


Run

 

I would think if the module had to be added to the list of modules that there would be an option or request in the Tech 2 to do it.
As far as I know there should not be any reference to module serial number in the message, just the module message ID. And that will be the same for every unit.

This U2107 says failed communication with BCM. There are a number of modules that communicate over the CAN bus. It could be any one of them. There should be another module that is failing to communicate with the BCM that should be setting faults too. I have seen this issue before on this forum. But I do not know if there was any resolution posted.

I think sometimes my Vident scanner sets the codes somehow. I clear them after they set. They do not seem to come back. And those codes are U2100 type codes that are setting.

 

thank you for the reply!!

im going to trouble shoot through the splice packs and go from there. Also I had swapped out the rear view mirror with a non onstar mirror, but I don’t think this is the issue. I’ll double check because according to the schematics onstar routes back through the VCIM.

What throws me off is the U2107 when the engine is running and it goes away when the engine is off. After looking at the schematics of HIGHSPERD GLAN. It looks like it’s a big loop through a tan and tan/blk wire.

Hopefully my logic is right here, but u2107 Service active handling goes away when the engine isn’t running is because EBCM is the last module in the GLAN, and checks out fine at the EBCM. However, when the key goes from ACC to RUN, the ECM comes online and now becomes the last module on the loop. Thus, there must be a break between the EBCM and the ECM. But wouldn’t the ECM a set a communication code as well?

any help is appreciated

 

As far as I know, it does not run in a "loop". It runs from the first module to the last module, daisy chained through the other modules on the bus. The first and last module on each end of the bus have a 120 ohm termination resistor in that module.The termination resistor is needed due to transmission line effects on the bus. Without the termination resistors, there will be reflections messing up the signals. Then communication will not work.

Each wire (twisted pair, tan and tan/black) should go into and out of each module, except the end modules where the terminaton resistors are located . There are separate connectors pins for both twisted pair wires, 4 pins. But the printed circuit boards have the CANHI and CANLO shorted together.

I would think that if the ignition is not on, the modules will not have any power and cannot communicate. My scan tool will not communicate if the ignition is in accessory. I have to hold the accessory button for an extended time in order to get the car to go to "on" mode without starting the engine.

I do not understand how there is any communication detected with the scan tool in accessory mode. I will go check mine again to see what happens in accessory mode.

 

Yes that’s what I meant. My apologies. The ‘ON’ mode.

I did more trouble shooting. I turned off the vehicle. I unplugged ECM C1 Plug. Measured resistance on the plug and it was 122. I would think this is a correct reading and there is no break in the two wires. As it would only be picking up the resistance from the termination resistor at the beginning of the first module the BCM. Measured at the OBD connector I had 60. Which means I’m measuring two resistors I parallel the BCMs and the ECMs which means no break in the wiring or broken pins.

When the Vehicle is ‘ON’ mode the U2107 code passes and no Service Active Handling is on.

When the vehicle is ‘RUN’ (engine on) the U2107 sets to Failed/Current and Service Active Handling is on.

any other ideas or testing I can do?

As silly as it seems sometimes I think it’s this rear view mirror I swapped out. My old mirror had the onstar and call buttons on it and this mirror from an 06 does not have them.

EDIT: just tried an onstar mirror with call button. That didn’t fix the issue.

Other idea I had might be the EBCM or BCM had to be reflashed. I just don’t think it’s this because the code and service active handling goes away during ‘ON’ mode

 

What other DTCs are set?

Your Tech 2 can display the EBCM hardware and software part numbers. It's under ECU Identification or something like that. What numbers do you have and how do they compare to the original?

 

Plugging in my scan tool seems to cause these codes to set.I clear all codes and recheck. No codes found. I shut down car and restart, no codes. I use a Vitron scan tool.

 

So I tried everything. Checked/cleaned every connector. Every wire for resistance and voltage. Every ground. New battery. New alternator (voltage was fluctuating so I needed it anyway).

nothing.

I searched through every single thread about EBCMs. So let me bust the false facts out on the forum by other users saying Ebcm didn’t need programming.

You can swap abs/EBCM and the car will turn on. Service handling will come on. It will lose communication with the BCM partially but it’ll run and the brakes will work. However SAH light will light up and this code will come on U2107.

Had my friend over at Chevrolet swing by and reflashed my EBCM. The light went away and the code went away as well.

thank you for those that helped me and replied to my thread. I hope my fix finds someone that needs help

 

Again, what were your EBCM hardware and software part numbers before and after? It shouldn't require programming if you're installing one with the same firmware version, but it sounds like yours didn't. Were the stickers on the EBCMs identical?

 

yes they were identical also checked the identification model information on my tech 2 for both EBCMs. Had the same calibration , software, base, and end model number. I checked before I returned the first one, thinking they might have sent me an 09+ one.

First EBCM was from an 08
Second EBCM was from an 05

Strange but maybe just flashing it helped make comm with BCM. Well if someone gets theirs to work from the get go, good for them, but if they have this issue a reflash might help

now I have to track down my final p0300 code and get this car back in the road. Thank you guys!