I am on my second LeSabre. I ended up with a 2003 four years ago that had a busted rear window and water standing in it, I fixed it up - turned it into my daily driver (NEVER failed to start or drive) - I drove it until it had 264K on it and gave it to my oldest son. I had bought a cheap "parts car" - a 2000 LeSabre with 179K that supposedly died and would not start again - last year. I had towed it to my shop, put the battery out of my 2003 on it to try it last year, and it started and ran. I put a battery in it, and started it up every time I was out at my shop. I decided to put it on the road - put front wheel hubs and control arms, and new tires on it. I drove it around without problems, and my wife got in it and it died within 2 miles. I had no fault codes or check engine light. It would not restart, I tested fuel pressure (it was good), hooked my Launch CRP129 up and everything looked good on a cursory check. It would start and immediately die. No flashing security light, so not a TR problem. I could spray starting fluid and keep it running as long as I nursed it with starting fluid. I disconnected an injector - found injectors constantly supplied with power, but the grounding for the injector pulse disappeared right after start up. My son googled it, and disconnected the air mass sensor. Still would not restart. I was messing with it, cleared the fault code, and it magically started and ran. I ordered an air mass meter and put on it. I have driven it several times now, including the 60 mile round trip to work one time without issue. I drove it to work this morning, made it 7 miles and it quit again. I had fuel on the fuel rail, so I knew the fuel pressure was good. No fault codes. I induced the air mass fault code by disconnecting it, then plugged it up, cleared the codes and it started and ran another 8 or 9 miles (quit within feet of the Mississippi river bridge). I did the same thing, induced the air mass fault code and cleared it, it started and ran the remianing 10 miles or so to work without issue.

To me, it sounds like an internal fault in the engine control module - ghost faults that can only clear after making a real fault code to clear are ODD. Any thoughts?