Driving on the highway a month ago, my 05 Grand Prix just shut down. A message came on the OBD that read "engine throttle electric shutdown" or something similar and then "reduced engine power". It turned over after a second key turn with 3 clicks and I drove away. I investigated on this site, and had my throttle body thoroughly cleaned out as well as the fuel injection system. The car was good for a week and it did it again and I took it to a repair shop and had a diagnostic run on the car. No codes, so the mechanic drove it and it did it to him. He then put it on the machine and 10-12 codes came up after it shut off a second time in the garage. He said that was impossible for all those failures to happen at one time. He pulled a GM service bulletin that identifed corrosion on the grounding wire as a possible cause. He cleaned it and the car shut down the next day. I started to think, this was happening with the air conditioning on. I've had the air conditioning off, and the car has been driving fine without the check engine light coming on or any shut downs. For many years, the car had the check engine light on and it kept throwing the "catalyst below efficiency" code, and I refused to replace the catalytic converter, while at times the car would hesitate when a I pressed the pedal after 10-20 mph. That same technician said nothing was wrong with my converter. He thought the ECM might be bad or going bad. Any thoughts? Thanks.