Cranks but no start

The car listed above is the CXL model. Vehicle belongs to my 95 year old mother-in-law who purchased it new, been garage kept and has only been serviced by Buick dealership

My wife was driving it today when it suddenly stopped running after driving maybe 3/8 mile. She tried restarting it but no success. I went to see if I could help. I could not get it to start either although the battery was spinning the engine vigorously. I checked to see if the fuel pump was running. It was, it would run for about 3 seconds like it should. Next I checked to see if it had spark. There was no spark at the coils. My thought was the Ignition Control Module (ICM) had failed. I removed it and went to O'Reilly's to get it tested. It failed their test so I purchased a new "Standard" brand module. I installed the new module and still no spark at the coils.

Then I noticed some "weird" things. First it had a "Check Engine" light on but my code reader could not retrieve the code. The reader would should that it was connected to CAN, display the battery voltage but state "No DTCs or Freeze frame data stored in computer. Memory". My reader is not the greatest but it has never failed to read either generic or ABS codes. Second, I noticed that when the engine was spinning vigorously while trying the start it, I had no signal to the tachometer, tachometer stayed at "0". Third and weirdest is that when trying to start it, the starter will continue to spin the engine for a full 2-3 seconds after the key has been turned back from "start" to "run'. I thought maybe the start or crank relay was sticking so I replaced it with another identical relay in the electrical box but no change. It continues to "run on" for 2-3 seconds.

My thoughts now are maybe the ECM has gone "south". What are your thoughts on this and what next step would you recommend?

Thanks in advance for your reply and for the help you have been to me in the past..

As an aside, I carried the new ICM back to O'Reilly's and had them test it. It failed but so did all the other new ones of different brands they tested. So much for their testing equipment. I have never had much confidence in their results and now have even less.. ..