Thank you for your question hope this helps.
DTC P1131 indicates the system is correcting RICH for an overly LEAN condition. The Heated Oxygen Sensor (HO2S) voltage is less than 0.45 volts. This is usually due to a vacuum leak after the MAF. It can also be caused by a bad PCV valve or PCV system hose. It can also be caused by low fuel pressure or a plugged injector.
To find a vacuum leak With the engine running listen for any whistling also with your hand reel the vacuum lines and fittings. You can also use a card cleaner spray all the vacuum lines and fittings the engine will reeve up when you spray the leak. (Be careful carburetor cleaner is vary flammable)Repair the leak you find.As for the PCV valve i would recommend replacing itlow fuel pressure or a plugged injector can be fixed by running a fuel cleaned at the next fill up.
You wanted to know what the bank 1 refers to hear is a numbering convention
Heated Oxygen Sensor Numbering Convention
Hope this helps