My car (smart 2008) has a rough idle so I replaced both O2 sensor because it was running rich,, scanned it with the torque app and it still showed bad test results for O2 sensor heater. I then decided to ckeck the fuses, turned car off, pulled key out, all fuses are good after checking the fuses I tryed turning the car on, it cranks but the engine won't start. I pulled the negative battery terminal for like 10 minutes then the car starts but it only stays on for about a minute then it starts to shut off slowly. I pulled the new Up stream sensor out and it was dark!!! Like pitch dark, I pulled the downstream sensor out and it was dark but not as much. I then decided to go to the dealer and buy the unique upstream sensor, it was $352 with taxes included by the way. I also bought a new bosh downstream sensor. When I got home I unplugged the battery then installed both sensors, car started and stayed on for a minute then started to shut off again. So I'm thinking it might be the ecu that resets when disconnecting the battery but for some unknown reason is preventing the car to stay on. Everything else works,radio, lights. Any ideas as to what the problem could be? Also my sparkplugs were recently changed but due to the rich condition they were dark so I cleaned them a little bit after this problem but still no start without disconnecting the battery and reconnecting it again.