My nephew has been a Nissan tech for decades and told me the ECM/Sensors are too sensitive on Nissan/Infiniti cars and it creates havoc when the Ethanol level content is incorrect and throws a light. It also burns out oxygen sensors way early too. Said only run "Top Tier fuel" and it will stop doing it. He was correct - I never had the MIL light issues again & I'm not replacing sensors like I was yearly either. The car never has had another sensor go bad in over 3 years.

All the car makers suffer from ethanol problems and they even tried to get it banned but failed. But they did help start demanding better fuel from the oil corps by starting the Top Tier gasoline program. Last year the US gov actually tried to raise ethanol content up to 15% minimum from todays 10% min. All the car makers told congress not to do this as ethanol is damaging our cars. Only flex fuel cars can really handle the Ethanol. They still wanted to raise it anyway because of the environmental issues gasoline causes.

So all the carmakers teamed up and simply told congress any new car that rolls into their dealerships with 15% ethanol in their fuel tank they'll just revoke its entire warranty on the spot. They can too as all cars say 10% max ethanol in manuals already. Only then did congress get the message and it finally cut their bs bill out.

Google "Top Tier fuel" and there is a list of gas corps who only sell this higher grade fuel. It ended all our cars problems within a couple weeks of use and have never returned. Even better, our Infiniti calls for 91 octane and you'd better well ran it too. But' ever since changing to top tier only I can run the lowest grade they sell without ever having spark knock or pinging at all like it used to when I tried it. MPG stays same for me with either grade. All grades are a top tier fuel at the top tier gas stations not just their highest grade and rarely has it cost me anymore than the trash other gas stations sell.