I've got this 99 that I'm working on as a racecar, but I've been fighting with Serial Data issues non-stop, any help you guys could provide would be greatly appreciated. The car will start and run, but it still has issues. I thought we had it narrowed down to a bad BCM, but I bought a used BCM that we were able to program with the Tech 2 for theft relearn and it's still acting weird. This car was wrecked, but the wiring wasn't damaged.

- Passenger carpet was damp, targa top has damage and leaks a bit, this is what led me to a different BCM, since it looked to have been wet before and alcohol cleaning did nothing.
- I've been working with the car hooked to a 2 amp battery charger to maintain voltage.

Main Issues:
1. With the STAR connectors unhooked, I can bridge between the BCM, PCM, and Data which allows me to talk to them and the car will run.

2. With the STAR connectors assembled, I can talk to any module EXCEPT the PCM, this gives me a 'Loss of Communications...' message.

3. With the STAR connectors hooked to everything but isolated from the IPC, I can talk to any module, including the PCM.

4. When removing RPO codes from the BCM using the Tech 2, I can select/deselect codes, but when I try to 'Save Options', I get a 'Loss of Communications' message, but the change is usually saved when I go back into the menu, is this normal function for this procedure or is it a problem? This behavior is identical with either BCM.

5. U1255 code is intermittent, it doesn't show up consistently with Communication issues.

 

Stig, I want you to just remove the 4 wire Star connector bus bar and see if that helps your corrupted serial bus issue.

 

The behavior is identical with the 4-wire bus removed.

A little more information, it's almost seeming like the bus line can't support more than a couple modules at once, if that makes sense? If I add modules back into the splice pack one by one (key off between) it gets to a point where communication goes away. With just the PCM and BCM I have no issues, I can add one more into the splice, but if I try to add any more than that it gets goofy. The 'No Comm' issue cuts in and out on the Tech 2, it will flash in and out of the PCM Data Display. Unlike what I thought in my first post, this issue does not seem to be consistent from one ignition cycle to the next.

I've tried both of our Tech 2's, with and without the CANdi module inline, and have pulled codes from the dash with identical results. The IPC dash readout showed NO COMM with the BCM and PCM on one ignition cycle, then on the next ignition cycle with no changes, it would read from the BCM but still NO COMM with the BCM.

 

You said "this issue does not seem to be consistent from one ignition cycle to the next"
That makes me wonder about the ignition switch contacts there is a thread on this repair.
I am no expert on vette electrical, but i was told to do it for another problem I had in my abs to eliminate that possibility

Here is the link to it:
http://forums.corvetteforum.com/c5-t...ch-repair.html

 

Thanks for the input, I cleaned the ignition switch when I got the car a couple months ago, so the contacts are still clean and greased (dielectric).

I think we've solved the problem, the STAR connectors felt loose, probably from being probed/prodded in a prior life, as well as my tinkering in trying to solve this issue with the metripak splice that I made to isolate modules. We cut off the STAR connectors, and joined key communication wires together in ring terminals, then bolted them all together, the issue seems to be gone. Ultimately, I plan to use several switches so that in a track environment, we can simply 'turn off' communication to non-essential modules while racing.

 

Glad you resolved it.

Why would you put dielectric grease (an insulating non conducting) grease on the ignition switch contacts?

That stuff is used where you have moisture and you use it "around" the "conducting path", not in it.

 

That's a good question now that you mention it, a write-up I followed said to use it, that's what I get for following directions

 

Leave it unless you have problems. It probably wiped off and will not be a problem.

The internet is full of ignorant people like me.