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Check engine light

I have a obd code p0172 and it says mass air flow system and defective o2 sensor, bank 1 running rich. Which oxygen sensor is connected to bank 1 of the engine so i can change it? I have 2 before the catalytic converter and 2 after.

Clean the MAF first before you do anything and reset.

Note: The code does not indicate it is a problem with everything listed, only that they may or may not be related to the problem. I think I would start with the MAF especially if your car may have experienced dirty air conditions or the engine air filter has not been replaced as often as it should or if it has had a K&N air cleaner at any time.

bank one is always the side with number one cylinder