Apologies in advance, this is a long post. But, I'm experiencing a pretty complex issue and I've done quite a bit of digging and troubleshooting that I need to go over.

As far as backstory goes, I experienced an unintended water intrusion to the passenger side which required BCM replacement, a thorough drying of the fuse box, and drying out of the Star 1 serial bus connector.

So far, I've completed all of this work at my house so I was able to perform a BCM relearn procedure using the ignition cycling method, but have not been able to configure the RPO codes yet in the new module. After performing the BCM relearn, the car started right up! No problems related to the serial bus. Next weekend, I go to start the car. Every dash light came on, along with a host of DIC warning messages and the car would not even crank. This behavior was very similar to what Bill Curlee describes in this post: https://www.corvetteforum.com/forums...-there-is.html

When I tried to pull codes, the DIC showed no comm. with any module. Based on what the DIC was telling me and Bill's post, I concluded that there was a major problem with the serial bus. Given that the Star 1 connector had gotten wet previously, I pulled the jumper and made absolutely sure the pins were clean and dry. After reinserting the jumper, I tried starting the car and everything was back online! I had communication with every module and the car started right up. About an hour later, I came back to try and start the car again and was greeted with a total loss of communication and no crank condition again. I have not been able to reestablish serial communication since then.

Before continuing with any further troubleshooting, I checked the basics that everyone always suggests first. My battery voltage is sitting at 12.8V with the car off, very healthy. I've also checked every single fuse, and none were blown. I have not checked my grounds yet, and plan to do that soon. However, I never had electrical issues with the car before this whole BCM replacement saga so it seems unlikely to me one could have suddenly gone bad at the same time as all this.

After many hours of research, I determined that the whole serial bus can be taken down when it's shorted to ground (forcing the bus low to 0V) or shorted to power (forcing the bus high to 12V). I started by measuring the voltage between Pin 2 (serial bus) and Pin 4 (chassis ground) on the DLC connector using my multimeter. I found that I was seeing 11V on the serial bus... NOT GOOD. This voltage did not change no matter what position the ignition switch was in. Next, I moved to the Star 1 and Star 2 connectors next to the BCM. By pulling the jumpers and measuring the voltage between each pin and ground, I was able to determine which data line was polluting the bus with high voltage. I got 0V on all pins except for one, the connection to the IPC (pink wire) which read 11V. Just to make sure that the serial bus was indeed the only thing preventing the car from starting, I jumped the PCM and BCM serial lines (light green and dark green wires). As expected, the car fired right up.

So here's where I am at this point: I've determined that the serial bus is being pulled up to 11V by the wire coming from the IPC which causes complete failure of the bus and prevents any communication between modules from occurring. I've done quite a bit of searching and a high voltage condition on the serial bus seems like a relatively rare failure mode compared to a 0V shorted-to-ground condition. I haven't been able to find any information on this specific problem. I plan to continue troubleshooting by removing the IPC, and visually inspecting the circuit boards for damage. I would love to test the electronics too, but I'm not sure how to go about that. I want to avoid replacing the entire IPC if possible, has anyone had this happen or heard of this happening before? If anyone has insight, I would really like to know...

What I'm still hung up on, is why I initially experienced an intermittent bus failure. It makes me think that something else unknown might be going on here. How could the bus function perfectly fine one day, and not the next? However, I don't really have much evidence to go off of besides the high voltage entering the bus from the IPC, so I will be pursuing that.

Calling all C5 serial bus experts, I need your help real bad on this one.

 

Good troubleshooting so far !!...if a module loses power or ground that power or ground “jumps” on that serial data wire and you see all those issues...I made a short video where I took 12 volts from my CAN breakout box pin 16 and plugged it into pin 2...all hell breaks loose !!...it won’t harm any modules but you can see what happens...I’d check the power and grounds for the IPC first.Another thing I would suggest is removing the bus bars off both splice packs and clean them with emery cloth until they shine..I had my horn not working a while back and when I removed the power wire it “looked OK”...hit the tip with some emery and it was fine !!

 

Thanks for the tips, I'll try cleaning all grounds before trying to remove the IPC in the hopes that I'll find something obviously wrong. Can't hurt to recheck all the relevant fuses either, something could have happened between now and when I last inspected them. Really appreciate your help on this!

 

Don’t know if you have the FSM for your model year but I can pass along my 2001’s electrical schematic if you need it !!..BTW you don’t have to clean ALL the grounds...just concentrate on the grounds for the IPC !!

 

Cleaned all the relevant grounds last night, there was a tiny bit of corrosion that I took care of so I'm glad I checked! However, it made no difference to the serial bus problem.

But, I have some good-ish news! I read my wiring diagram wrong, and the Pink wire at the Star 1 serial bus connector is actually coming from the RFA module. I misread "instrument panel electrical center" as "instrument panel cluster". Very relieved my dash seems to be okay! I will continue troubleshooting to see if the 11V on the serial line is originating at the RFA module or the interior fuse box. From the wiring diagram below, it looks like the serial line passes through the fuse box and there is a pretty good chance the fuse box is still a bit wet inside and could be causing the short. However, I will make sure to double check it's not coming from the RFA module.

Opening up the fuse box seems pretty daunting (referencing this thread: https://www.corvetteforum.com/forums...x-autopsy.html) so I'm debating whether to buy another and just swap it in, if it turns out to be the problem.

 

This is from my 01 FSM...don’t know if it will help ??

 

Thanks for the diagrams, definitely a help. I'm 99% sure there's something wrong inside my fuse box at this point. I can see the voltage on the serial bus dance around when I shake the box, which is enough evidence for me. I was able to find a C5 being parted out locally, and I'll be picking up a fuse box from it in the next couple of days. Getting closer to solving this!

 

Good luck, keep us posted on the fix plz.

 

My replacement fuse box finally came in today. I swapped it into the car and.... everything works as it should! The serial bus seems to be working perfectly, I have communication to all modules and no codes present. It seems like there was definitely some residual moisture in the old fuse box causing a short between power and the serial bus. Thank you to C5 Diag for all your help, this one definitely pushed the limits of my troubleshooting skills. Hopefully this thread helps out others with serial bus issues, although my situation seems to be somewhat unique. If it looks like your RFA module is causing serial bus issues... check your fuse box too. I certainly did not expect a portion of the bus to be routed through it.

 

Does the fuse box plug into a main connector or is it part of a wire harness? How difficult was it to replace?

 

There are 3 large connectors on the back side of the fuse box. They have a bolt through the center of them to lock the connectors in place. There is a 4th connector under there also that clips in and the main power in connected to a bolt on the top of the block.
So relatively easy to remove taking your time. It is a must to disconnect the battery before removing the fuse block.

Gary

 

As Gary said, there are the 3 large connectors on the back. I found them somewhat difficult to remove due to the size, each one took a little bit of fiddling with a flathead screwdriver to pry it away from the box (after loosening the bolts). In addition to the main power cable that needs to be detached from its mounting stud, I had 3 more conventional connectors near the top that are easily removed by depressing a locking tab on the connector housing. In total, there are 7 wiring harness connections that must be removed before pulling the box. I had my passenger seat removed in order to make access easier, and found that lying on my back with my feet sticking into the rear compartment was the most comfortable position for this job haha. Definitely disconnect your battery before starting work.