The answer is "Crankshaft Position Sensor".
Yours is almost the exact story I was telling anyone who would listen to me when my car's engine was dying almost every day. Most times it was when I was on my way home from work (20 minute drive).
There was no warning and it almost seemed that someone was turning the ignition switch off.
The mechanic I found took the car and did diagnostics (no problems according to the computer). After two days he finally got the engine to die, but instead of troubleshooting, he started it up again and it wouldn't die again. The following day, it died, he did the troubleshooting, decided the ignition module must be intermittent, and replaced the ignition module. The car started and ran fine. The next day, he called and I thought he was going to tell me to come and get my car but, instead, he told me that he thought my car was possessed. After the laugh, he told me that the engine had died again and that the only thing left to look at was the Crankshaft Position Sensor. He removed the new ignition module, installed a new Crankshaft Position Sensor. The car started and the engine didn't die.
The next day, he started and ran the car and the engine didn't die, so he called and told me to come get my car. It has been over three years now and the car has not failed to start, stay running, and has not died except when the ignition switch is turned to the "OFF" position.
Good luck with the other problems. They may or may not be corrected by changing the sensor. Also,
GM didn't do us any favors by removing the heat shields and replacing them with lousy ignition wire clips. I am still steamed about that one. Not much of a fix.
Wednesday, January 20th, 2021 AT 10:49 AM