The most common cause of this DTC is vacuum leak or exhaust leak. For the V6 and a code affecting bank 2, also think exhaust leak from cracked manifold.
Consider that if the MAF were at fault, it would affect both banks. So when the DTC code is from one side, focus first on causes that can affect one side.
However, it never hurts to clean the MAF.
H40 DTCs P1131, P1132, P1151 AND P1152: UPSTREAM HO2S NOT SWITCHING. DTC P1130: FUEL SYSTEM NOT SWITCHING AT FUEL TRIM (RICH OR LEAN)
HO2S-11 = DTCs P1131, P1132 and P1130
HO2S-21 = DTCs P1151, P1152 and P1150
Excessive fuel pressure.
Leaking fuel injector(s).
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Contaminated fuel injector(s)
Vapor recovery system
Air leaks after the MAF.
Vacuum leaks (vacuum lines and gaskets).
Restricted air inlet.
Improperly seated engine oil dipstick.
Stuck open EGR valve.
Exhaust leaks before or near the HO2Ss.
Check intake air system for leaks, obstructions and damage.
Check air cleaner element, air cleaner housing for blockage.
Verify integrity of the PCV system.
Check for vacuum leaks.
2003 GT Convertible (sold)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.