I have a 1997 F150 4.6L engine vin code 6. I've got a P1151 code (run lean HO2 bank 2 sensor 1) I done just about everything I can think of to solve the problem. Replaced HO2 sensor, replaced plugs & wires, replaced fuel filter, cleaned MAF, cleaned injectors, cleaned EGR and it's system, PCV valve, and went through all vacuum lines (replaced two ( PCV vacuum line and throttle body to EVAC on fire wall.
I'm at a loss. If anyone can help I'd be so so unbelievably grateful!!! PLEASE ANYONE!! Oh, and checked for vacuum leaks on the intake with brake cleaner. Please understand that I didn't do all these things in this order. I started with the small stuff and worked my way into the more complicated things.

 

A code P1151 may mean that one or more of the following has happened:

Electrical:

Short to VPWR in the harness or HO2S
Water in the harness connector
Open/shorted HO2S circuit
Corrosion or poor mating terminals and wiring
Damaged HO2S
Damaged PCM

Fuel System:

Excessive fuel pressure
Leaking/contaminated fuel injectors
Leaking fuel pressure regulator
Low fuel pressure or running out of fuel
Vapor recovery system

Induction System:

Air leaks after the MAF
Vacuum Leaks
PCV system:
Improperly seated engine oil dipstick

EGR System:

Leaking gasket
Stuck EGR valve
Leaking diaphragm or EVR

Base Engine:

Oil overfill
Cam Timing
Cylinder compression
Exhaust leaks before or near the HO2S(s)

Read more at: http://www.obd-codes.com/p1151-ford
Copyright OBD-Codes.com

Bank 2 Sensor 1 is the front O2 on the driver's side.

 

@Charles G , I often use a couple of resources for OBD-Codes as one may have some information (not necessarily different) but other clues, in addition to that mentioned above that can be helpful. Such seems to be the case here with P1152. http://www.autocodes.com/p1151_ford.html gives a pretty nice detailed description of the Monitor Test that is failing to run successfully for two drive cycles. Several things I wasn't aware of - like it seems this Monitor test failing may be a pre-cursor to a P0174 Code if the problem continues.


Good Luck