No Communication! Car Runs!
This car starts and drives but no communication with BCM (gateway), ECM, TCM, Parking brake control module, multi axis acceleration sensor, headlamp control module and FPDM. Dashboard was replaced along with ipc, radio and other modules because the original dash burned up. Waveforms on hsGMlan looks good from dlc. Back probed gateway and waveform still looks good. So I back probed the headlight control module but the waveform still looks good. Still no communication. What am I missing?
On GMlan can you communicate on those modules? It wouldn't hurt to pull some things out of the network by disconnecting the JX200 comb lower left of dash, or JX202 and see if that helps . I've had huge issues with network issues with GM with Onstar and telematics so I usually pull those out first. Connectors are usually in the bulkhead by your left food A pillar. It's been helpful to me to…
tried disconnecting both 1 by 1. NO change. But loses comm. to low speed gmlan modules
Just had one of these same problems on an earlier model GM. Vehicle was scheduled in for O2 sensor code to be diagnosed and repaired. Car was scanned for code at time of appointment. This means it had all communications. When vehicle arrived a couple of days later confirming the code, no communication was experienced. Security light was illuminated too. Car started drove and ran fine. Spent lots…
Sometimes the easiest solution is the best solution.
This may seem crazy, but… a few times on this style GMs after trans installs, or major work… I've had good 60ohm resistance, no short to power and no short to ground on CAN ckts. Ive disconnect then reconnect BCM connectors accessible from passenger side and then boom, everything is back, and no return of problems. Im not sure if it's a connection issue or what… Just throwing that out there…
Yep. As I stated, all test results were fine on the situations I had this. I was pulling my hair out. Unplugging BCMs was an act of desperation, and it literally worked. I also found a few Identifix hits stating the same. It may not fix your issue, but again, I thought it was worth mentioning.
Ah yes I did swap another bcm to see if it will communicate to no avail, so I re-installed the original one. So disconnecting the bcm makes no difference.
There is no gateway per say, the BCM only acts as a passthru on this vehicle. Did you try another scan tool? If the waveform is good at the DLC then communication should be present.
Agree William, but on the subject of the BCM being the gateway/bridge/translator between GMLan HiSpeed and GMLan LoSpeed….if its not the BCM then what module performs this function on this vehicle?
So the BCM does move some but information from one network to another but this is information is very specific. Usually relating to Tach or vehicle speed etc so the cluster can display it, but to call it a gateway is misleading. If this were true you could call the EBCM the gateway between the GMLAN HIGH SPEED and CHASIS HIGH SPEED. The information transfer is very limited. Now our newer Serial…
Hi William, I definitely agree. Serial data gateway and similar terms really weren't a big thing back in 2013 for most if not all manufacturers like they are and have been for the last 5 years, say. Specific to the post however, he is referring to can traffic amongst like modules (high speed) which wouldn't involve the BCM to translate down to a low speed single wire module. It's possible he…
That's not the issue. The pins are fine. back probed the bcm and also the headlamp cm, but waveform was still fine. I even back probe hs gmlan+ on the HLCM and hs gmlan- on the bcm input wire and the waveform was still fine. At this point I will diagnose the following codes and see where that leads, b1451:04, b144b:04, b3122:05, b1370, c0161:5a and u0074
I would look at B1370 first...usually refers to too much of a difference between 2 different voltage feeds to the module.
I started on that until I found out that dtc b144b:04 takes priority over b1370. I'm going after b144b, 1451 and 3122 first.
I had one like this the other day when using the Autel (don't remember which model Autel). Fired up GDS2 and it read everything fine. Went back to the Autel and checked pin tension on DLC pins….still no communication! I've read other people's reports of the the same with GM and Autel.
Did you check the resistance of 6 to 14 and 12 to 13 on the dlc. They should both be 60 ohms. If you have 120 ohms on either I have used a 120 ohm resistor to bring the total resistance down to 60 ohms and you could get communications up and figure where the break was. Resistance checks should be made with the battery cable off.
Does terminal 16 have battery voltage and do terminals 4 and 5 have ground on the dlc. As Kerry Sutton said have you tried a different scan tool, no bent pins on the connector of your scan tool and good terminal tension on the data link connector.
In the rear going up to the trunk area these cars the wiring gets corroded and the wires break or a few strands still remain connected, ive seen it creat alot of havoc on the buss, intermittent communication. Might not be it but its a place to look. Follow the wiring up to the fpcm and around the rear end
Open up the wire loom and look for wiring discoloration and corrosion. Id bet your prob is in that area, 3 times this has fixed it for me
you're onto something. i thought about checking there because someone before me had been back there trying to fix the trunk that wouldn't open. Now that you mentioned it i'll make it a priority. Thanks
I'd suggest to reboot this car (disconnect and drain capacitors) and see if your communication comes back. If not, jumper the high speed LAN at the BCM and make sure you can talk to all the other modules on the high speed bus first. If that proves out ok, you are only after a loss of BCM communication issue. It is not a gateway, btw.
You replaced several modules, were they new or used, was the bcm changed with a used unit?
I didn't replace anything on this car. The owner said the dash had been replaced along with several modules. During my investigation i found a used bcm in the car but not installed. So my assumption at tis point is that the bcm installed is the original one. The IPC is brand new unprogrammed but it communicates.
Matthew was right, the solution was simple. It's the wrong harness they swapped in the car. But before I go further I have to clarify something for the people that was saying the BCM was not a Gateway. I have an engineer friend who works on CAN all the time. He said to me before that a gateway is any module that allow communication between other modules. From the diagrams it's clear that the BCM…
Hindsight is both a terrible and wonderful thing. Was it simple solution? If you say it was missing or crossed wires, to the layman that's a simple explanation. To those of us that are following you through this repair I'd say you did a great job. It wasn't easy. lets look at some of the things to get the result. Knowledge of data bus circuits and high speed and low speed network…