I could use some help. My 02Z has been having intermittent problems with its one-wire bus, causing the appearance of a multi-system failure (traction control, service engine, no fuel, etc.). The problem comes and goes, somewhat correlating with ambient temperatures but not consistently so. I haven't figured out why it sometimes fails and sometimes works or how the weather seems to be affecting it.

I checked and cleaned the star connectors in the passenger foot well area, but this didn't help. I cleaned the connection in the passenger door connector, and this seemed to help for a while. When I looked at the driver's door connector, I saw that the pins were angled slightly inward for a surer connection, so I did the same to the passenger door connector pins. This helps for several days. Yay! But...the problem is back. I've checked many of the chassis grounds (the ones I can reasonably reach without much fuss--I may need to endure some fuss, though) and look reasonable. The battery has been replaced, so it's not a low-voltage issue; unrelated to this problem, my old battery was not getting above 12V so it needed replacement anyway. The only thing of which I am aware that I haven't checked are the seat connectors. (Do I need to remove the seats to access and/or isolate these?)

Have I missed anything? I've searched CF quite a bit on this issue, which is how I learned of the above things to check and clean. Is there more that I've missed? I still need to drag out the manuals and see where that bus goes, but the codes (several Uxxxx codes, plus "no comm" to PCM) suggest it goes all over the place. I'd certainly appreciate any help you guys can offer, especially if your experience suggests a troublesome spot I haven't yet checked.

 

One thing I haven't tried is isolating subsystems, one at a time, via the star connectors. I'll add that to my diag list.

 

If it were me,, I would pull the STAR Connector top (the one with four wires for the LDCM, RDCM and SCM) and leave it disconnected to see if the issues goes away. You can reach the seat connector if you raise the seat all the way up.

The seat connector often gets damaged because it the low hanging fruit under the seat. It can and does cause issues on the data buss.

If I were you I would also consider cleaning or replacing your ignition switch. That will eliminate any low voltage issues on the IGNITION POWERED circuits.

-C5 ignition Switch repair - http://forums.corvetteforum.com/c5-t...ch-repair.html

BC

 

Good stuff, Bill! Thanks!

 

Well, it's not the four-wire star connector or its subsystems. It's not the seat connector either.

I've narrowed the relevant codes to:
PCM No Comm.
TCS U1000
BCM U1255
SDM U1000, U1016
RFA U1000

These seem to be pretty much PCM-centric, so I'll concentrate my efforts there. Looking at the DLC schematic, the PCM is pin B, dark green. Maybe in my earlier attempts to isolate it to the right door connector, I may have inadvertently mangled the PCM's connection to the DLC.

 

Pulling the shorting plug from star connector #2, isolates the seat as well....no need to do both.

The PCM connects directly to star connector #1.....not the DLC.

 

That's what I meant. Perhaps I'm using the term DLC incorrectly. I associated "DLC" with the one-wire bus and therefore the star connectors as if these were all functionally synonymous. I welcome correction, though, as I'm still learning lots (for which I am very grateful to CF and its abundantly helpful members).

 

DLC = Data Link Connector. Located under the drivers side instrument panel. Where you plug in a scanner/code reader. The "one-wire bus" you referred to, is known as the "class 2 serial data line".

 

Here are the schematics that you need to see how everything works. Some of the gages and functions on the IPC are imulated and are digital signals transmitted over the DATA BUSS

 

This weekend I was able to do lots of diagnostics to narrow down the problem. It seems the problem is the PCM itself, not anything else on that data bus and not any connectors or wiring.

 

Read this post and do the same.. Read the resistance of each module and post here.

http://forums.corvetteforum.com/c5-t...on-on-dtc.html

BC

 

I already did the isolation as prescribed (IPC, BCM, and PCM only), and the same codes persisted. I'll try the resistance-to-ground measurements tomorrow and see if there are any anomalous lows (<10K)--or infinite highs, for that matter. If I do find a low reading (presumably it will be in the PCM), does this suggest a short inside the indicated module, possibly caused by a blown component? If not, what is implied?

 

Well............. If you find a reading out of line with the norm,, disconnect that module at the module and read the wire from the STAR connector to the connector and then read the disconnect module buss pin to the ground pin on the module. The LOW reading will be apparent where its at.

BC

 

That sounds reasonable.

As part of my diags today, I checked continuity from the star connector to the PCM's connector (pin 58 on blue). Looked fine. I even went so far as to open up the PCM on the off chance I could see a blown component, but it looked good, and continuity from its connector through its initial, internal RC was good. Given the IPC-BCM-PCM isolation and the PCM-centric codes, plus the good continuity outside and just into the PCM, I surmised the problem probably lies within silicon in the PCM. I expect a resistance-to-ground test will likely confirm this.

 

For the sake of closure...

After all was said and done, everything pointed to a bad PCM. I put a new one in and had it programmed, and that fixed everything.

I thank you, Bill and Lucky, for your help!

 

I can't believe this, but all the symptoms have returned, even with a new PCM. I'm turning it over to the pros but will post the final resolution (after it's worked for many days without issue) for others who might encounter these symptoms in the future.

 

Well,,,, If your NOT looking very closely at any and all FEMALE PINS in the data buss circuit and door power plug, your doing your self a disservice. Shop time will get VERY expensive with an intermittant issue.

Recheck your door power connector and make sure ALL the female pins are not spread apart. You really need to fins spare male pins and insert the male pin into any female pin that is in the circuits that need to be checked...

Use a male pin of the correct size and CHECK THOSE FAMELE PINS!