Long story short, saved a 99 FRC from a dude in Texas who did not care for the car. After cleaning the blood, **** and tobacco chew out of it, new ignition switch, keys, stereo, yada yada the car was great for months.

Part of the mis-care included a bad OP sending unit, and a missing PCV system that caused the car to leak a quart of oil over a weekend. In order to clear tech for a track day today I had to clean most of the **** off the engine and that's when things went south.

I used very low pressure water and kept it away from major electronics, immediately fired it up and let it idle for a half hour to dry off as I was on the phone with a customer. Everything was cool and I was set to participate.

About 5 hours later I gunned it getting on the freeway and had slight traction loss and that's when the lights popped up. Checking the codes yields something sometimes, and No comm. at others.

At first if I hit the TC button immediately at start up, and turning it back on, they would stay off, but that only lasted half the day.

Fearing I soaked it somehow, I removed the battery, removed the EBCM connectors, cleaned the pins thoroughly (they were spotless anyhow) applied a **** ton of dielectric grease, removed all the grounds in the bay, sanded with emery cloth, **** ton of dielectric grease, removed the battery (again, it was new as part of resurrecting the car and doing the stereo) load tested and checked out, strong charge. Checked voltage to all related fuses 5, 52, 53, and all are proper, changed the fuses anyway.

Codes are

PCM
P1689HC

TCS (when codes show)
C1255H
C1276HC

I am drawing a blank for the abbreviations of the other two systems but a U1040H, U1096H, U1016H, U1064H show.

Clearing them does nothing, they come back immediately, except the TCS codes, when I start it I get C codes, but if I clear them before shutting the car off, is when I get the No comm. either sitting or driving.

Am I looking at a bad EBCM or is there something I missed?

 

Bueller?

 

The first step of the troubleshooting procedure for the C1276 code is to check G108 and G101. That would be a good place to start. Do a search for ground locations if you don't know where they are located.
The P1689 is essentially the same code as the C1276. CKT 464 malfunction.

If you have to troubleshoot the U codes start with the U1040, Loss Of Comm With The TCS. There is a TSB stating that when the other three codes are all set, it can be caused by another comm issue.
Check the wiring and data star terminals. Bill Curlee has posted picture of the data star connectors so if you search you should find that as well.

 

Your battery might be low

put it it on a charger or battery tender and see if this corrects the issue.

when you start your car the dic should say "corvette by Chevrolet" if your battery is low it won't say this and could cause the ecm to throw the code you mentioned due to low voltage ... Hope this helps if not others will chime in

 

I did miss the TSB info doing my research, thanks. But as stated I removed all the ground connectors in the bay, cleaned and reinstalled them, in fact after the stereo install I have cleaned all of the ground locations in the car and they were spotless to begin with.
During all my troubleshooting I had it on a charger, and as I first posted the battery is new, load tests pass, charge system passes, car exhibits the "Corvette by Chevrolet" at start up and my aftermarket navigation retains all its settings, all fuses pass their voltage tests as well.



I did not drive it the past two days as I was irritated with it so I drove my truck. When I drove it today I pulled the codes again and still have the P1689 but now I have a consistent TCS No comm. And it seems now I no longer have interior lights and the fuse that powers the relay is not blown, possible relation?

 

I'm not seeing the connection between the interior lights and the P1689/C1276. That's not to say there isn't one, just that I'm not seeing it. A power distribution problem maybe? The lighting is controlled by the IPC with the BCM providing the ground path for the minirelays in the IPC. The wiring for the PCM and EBTCM codes are a direct connection between the two.

Have you done the voltage and resistance checks listed in the troubleshooting procedure for C1276? If not start with the ABS power and ground checks at the bottom of this post.

Can you verify which system cannot communicate with the TCS. It's not listed in your origin post.

Also have you checked/cleaned the data star connectors? This thread has some info regarding the star connectors. (with pictures)
https://www.corvetteforum.com/forums...al-issues.html
You can try cleaning them and see if the U codes will clear. Also check the serial data line from the star connector to the EBTCM. Star Connector 1, Cavity E to C102 cavity R, to EBTCM Connector Cavity 10.
I think I would do this after the ABS Power and ground checks.

Another thing you can check is the ABS power and ground distribution. It looks like you have done most of that but have you checked the voltages at the EBCM? Pay special attention to the ignition positive voltage level. See attached file.

 

Well the interior lights was just a shitty chinese fuse, twisting the fuse would cause the contacts inside to shift to work, and not work. I just mentioned it in case it could have been relevant.

I did inspect the data star connectors while I was doing the stereo trigger wiring. Just for ***** and giggles again, when I changed the courtesy lights fuse and they're still spotless.

I haven't had a chance to run the checks, this was my first chance to get back to the forum even. Tomorrow I should have a clear day and I'll run what you posted and check the other systems as well.

I did drive it to downtown and back today, and while the car is running I always get a No comm, and occasionally now when I shut it off I will see the 1255 but nothing else.
EDIT: I just went out and pulled the codes again, here's what showed.
PCM
P0801 HC
P1637 HC (these two seem to pop up when i'm pushing the sub hard, I'll install a capacitor soon, but figured I would mention them)
P1638 H
P1689 HC
TCS
C1255
C1276HC
BCM
B2528H
B2587H
B2592H
SDM
B1001H
U1040H
IPC
U1040H

Clearing the codes caused the C1276 to come back instantly, before starting. I know the likelihood of it being a wiring issue after I washed it is low, but I will certainly check everything and report back.

 

Cleared all the codes and took it to the gym tonight
These are the codes that repeated
PCM
P1637HC
P1689HC
SDM
U1040H
IPC
U1040H

Will run tests in the AM.

 

So sometimes you get C1255 and sometimes you don't? That is an internal malfunction of the EBTCM. Usually you get the C1255 and your all done. Do your checks to make sure it isn't a low voltage problem. Make sure your stereo system isn't powered when you are doing your tests. If you don't find anything it is probably a failure of the EBTCM. Unfortunately the EBTCM is not repairable. Your only option is to get one from a recycler, if you can find one, and they go for crazy money. Also I wouldn't use the dielectric grease under the ground connections. I prefer just to have a good metal to metal connection.
P1637 and P1638 are generator ignition voltage and duty cycle fault codes. If those only pop up when you are running your sub you are exceeding the limits of the generator.