OK, have been going over the electrical schematics this morning (sheesh these modern vehicles are intense!). Seems like there could be a compromised Class 2 data line from the ECM to the data line splice block, easy to check. The transmission TCM communicates with the ECM via a high speed data bus separate from the Class 2 data bus so the vehicle continues to drive well. Also, the TCM communicates to the the Class 2 splice bus for vehicle speed so that seems to be why the speedo works. I'll post my findings on the ECM to Class 2 bus splice once I check it.

How are you checking/testing these?

1st, check continuity between pin 48 of ECM C2 & pin B of SP205 under the dash. If good, reconnect C2 and start & scope the pin B connector to see if there is data coming through...that'* where I'll start..

You should load test them. A simple ohm test will not find many problems.

Point taken. I feel so stupid. Opened the hood on this thing first time since I asked about ECM location. And there it is right up top. It'* much smaller than the other ECM'* I've known from the past.

So, been messing around with the Buick over the last several days with the warm weather:

1) Removed the lower dash panel & upper dash surround for access.
2) Checked the Class 2 serial data connection between ECM C2 Pin 48 to the dash panel pin B1- Connection is solid, not open.
3) Swapped dash panel back to the original w/ correct mileage- no joy, behaves exactly the same as the replacement. no gauges, only speedo and that data appears to come from the Transmission Control Module (TCM) not the ECM.
4) Found 2 other systems that do not function & have a connection to serial data & the ECM directly are the A/C compressor clutch & the Satellite radio (XM) probably for the OnStar data.

Beginning to question the ECM or maybe it'* programming?

Thoughts?

Thanks,

Mark

I don't think ECM issues would affect the compressor clutch and satellite.

Curious: Does it still have the original ECM in it?

Hi, yes the ECM is original. For sure the AC clutch relay signal comes from the ECM, the XM isn't clear but the diagrams show serial data connwction.

This feels like one of those times where the issue is so messy that the symptoms steer us off-course.

Back to basics:

1. Car was fine
2. Squirrel!
3. Car broken
4. Dealer fixed some, and knows it didn't fix all
5. Dash swapped for same result
6. Dash swapped back for same result

. . . if I have the situation right.

If the damage from Step 2 is known to be incompletely fixed, it'* not likely a new and unrelated problem. It is likely a leftover from step 4.

Can you get us pictures of the work done in Step 4?

Basically, yes the outline is correct. Dealer tech did a pretty good job of retaping the hardness, not much to see. I'm going to remove the air cleaner assy and look at the harness where it passes under the air cleaner. That harness ultimately goes to the dash and would be a perfect spot for the damn rodent to feast as the damn thing surely came in from underneath the car.