GM CAN Bus Wiring 

The length of this is right up my alley, the content, and how to apply it to my knowledge base still escape me. Will keep plonking along with my test light and multi-meter. Best of days to you and yours Danner !

I just ran across a video by Enovation Controls "CAN Bus Properties and Troubleshooting" where they have a simple (3 device) CAN network set up that they can create faults and show testing. Very informative. Industrial but still useful for automotive.

Great content as always Paul. Interesting to see the difference in design concepts. I am a Mercedes-Benz tech from the UK and they do it a different way again.

Always enjoy a good informative video...

The only thing about the latter design is when you unplug one module in the line. Even though all are wired in parallel, since the connections are internal, you lose everything downstream of the unplugged module. That could be an advantage if looking for a short to ground, since you can divide the circuit in two and see which side the problem is on.

Thanks for sharing Paul... Cheers.

Thanks for sharing SD👍 Important stuff to keep in mind😉 Stay Safe👍

Great again Paul, Thanks a lot

That was great info Thanks 👍

had the question for a long time unanswered. thanks

Thanks Paul! this came at a great time. I having problem with CAN on my EBCM on my 2011 Volt. This may help me figure it out!

Thank u mr Danner

Here is the thing. What you say about these circuits being equivalent is true for DC signals. But for data transmission circuits they are very different. The physical network should be a pair of wires that are terminated at each end, GM uses 120 Ohms, this commonly called a data bus. The network can have several modules that are on the two-wire bus each may receive and transmit on the bus, one at a time. The terminating resistors are used to prevent electrical reflections when a signal travels over the bus and hits the end. When the signals hit the end of the bus the resistor absorbs that energy. Otherwise it bounces back in opposite voltage and distorts the next transmission signal. The GM bus operates at 500,000 bits per second so the data lines will change polarity in as little as 2us (microseconds). to put data on the bus one module at a time turns on it's transmitter and flip-flops the polarity of the voltage on the wires. A "1" signal might be White=4V, Blue=1V and a"0" would be the opposite White=1V, Blue=4V. All the other modules listen to the signals and either do something with the data or ignore it if it is not addressed to them. But switching the signals every 2 us means there will be lots of reflections, one from each end. These reflections are very real and can confuse the other modules as the reflected signals compete with the real signals sent out by the active module. Now if you use a Y shaped bus you have three sources of reflections, even worse. Putting a third terminating resistor on would help but having 3 terminating resistors present may overload the transmitters of the modules on the bus and maybe kill them. To really diagnose this type of signal bus you really need to use an oscilloscope to see what the signals look like but most of us don't have one. Unplugging a module is a viable means of checking what works and does not but it will sever the bus. The severd bus will probably work with only one terminator present, but it may have some errors in transmission (which you probably can't see even with a scope). It is also possible that a module has a burned out driver that could either be an open circuit and not interfere with (or be seen on) the bus or could have shorted internally and could kill all communications.

Thanks danner. Never got too far into CAN BUS systems before I left the automotive industry to be an industrial tech.

OMG the smart level just got higher than the moon....

Thanks, Dan. I worked for many years in elevator systems and we have similar networks for all the buttons and signals that run the length of the building. With networks you modify them at your peril since lots of engineering goes into making one that works well. Do you know where I can find a copy of the complete CanBus CTS schematic? I'm working on a LFX swap to a Fiero and finding the connection info is next to impossible - Unless you want to spend $500 for a Helm manual.

Hello Dan I have a 04 cadillac sts communication comes on and then doesn't come on but I still get 121 ohms when the whole car is working properly🧐🤯🥴😵‍💫😔

I have question regarding the LIN bus, I remember from classroom video that CAN bus are bidirectional means that communication is coming in & going out. Let us say there is a control module which has power & ground in perfect condition, than even if it does not have communication coming in , it must have communication going out. So in a control module if I remove the whole wiring connection & only connect it with power supply/ ignition & ground & I do not connect any other wire, it must have communication coming out of it .... Now the lin bus are unidirectional, does it mean that it only sends information in not out , so the test that can be done in CAN should not hold true here ? Please correct me if I am wrong thankyou

So my FPCM has 2 tan #2501 wires and 2 tan/blk # 2500 wires. I can swap between the pin outs for the tan/blk and have no affect on communications ? I'm tryingg to figure out why my Exhaust flap isnt getting its ground signal to close. I can manually ground but the ECM or the FPCM isnt communicating and I'm not sure why.

Well that sucked im paying for it and dont see it,😂😂😂😊love you all keep up the good work, im getting my phone number changed hope ill still see you

hai sir nice job sir ...sir i have problem with ford Ecosport 2014 if i disconnrc abs module,,an engine and transmision was no trouble code ..but car in idle position not run....if i connec abs module engine and transmision was errror...what problem you thinks sir?? in from indonesia sirr...

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I'm checking the ohms resistance on the can bus from 6 and 14 on the obd2 I am getting 0 ohms. I have a code u0073. Where do I go next

Is there a way to test the GM CANbus FROM control unit to verify that it is communicating not just passing it through?

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I'm confused about the series parallel series circuit, but I guess that's not important. LOL. I get the message. What are the MG8-9/MV7 circuits?

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Where is the best source for wiring diagram

Hello. I have a problem with a can bus. No u codes. I can communicate with all the modules but i can't get live data. As soon as I try read the live data on any module, the scanner takes me out and display a message of no communication. I have literally done everything. I don't really know what else I can do to diagnose the can bus system.

3 place😁👍

Daisy chain topology.

Are you working in GM before?

If I understand correctly, both circuits are electrically identical (as long as all the modules on the GM circuit) are working. If a module on the GM-style goes bad, then the entire CAN bus goes down? Correct?

I will fly you down to Florida and pay all expenses' if you can fix a 2000 Ford Windstar severe motor vibration.

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