Getting P1151 and P1131 codes on my 98 Ford Taurus. ''Lack of HO2S-21 and HO2S-11 Switching, Signal Low Input. Does this mean the O2 sensor(s) is defective, just durty, or some sort of vacume leak, or??

what engine is there, , size, displacement in liters or CUInches.
3.8L V6?
p-0135 is a uSA federal code, all P0xxx are.
P1xxx are care makers owned codes, means do not read lies on the internet about, p1,p2,and codes only read your service manual
learn that bad heaters are to be fixed first 02 replaced or wires melte there..
HO2S-11 Heater Circuit (Bank 1, Sensor 1) bad O2, front of CAT sensor bank 1,
aka. upstream.
bank one is cylinder #1 bank side.
#1 cyl is the most front cylinder on all v6 or v8.
all this is me reading your service manual to you.
p1132
Lack of HO2S-11 Switching, HO2S Signal High Input this fails because heater is dead. so is moot here, later yes now no.
0135 first.

p1151

Lack of HO2S-21 Switching, HO2S Signal Low Input bank 2, sensor 1. (may be caused by above otherS.)

H-hear, O 2 means oxygen sensors
11 is bank1 senser.
12 B1S2
21 b2s1
22 B2S2
SEE?

https://www.engine-codes.com/p1131_ford.html
https://www.engine-codes.com/p1151_ford.html

all codes are OBD ll are available online for free. google your codes.

bank 1 sensor 1 lean code. Check vacuum lines first. Could be egr leak also. Most vacuum lines run on the back side of the engine on these. Most common fail is the PCV 90 degree elbow. On the passenger side.

Hope this helps you or future parties of intrest. P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1 P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2 I would get under your stang and gently clean outside portion of o2 sensors using a scotch brite. Also if you have so dielectric grease pull electrical connections to o2 sensors clean them and add grease. These trick eliminated the o2 sensor OBD1 codes on my 1987 Ford mustang gt

I will try to paste an article for you. Several sources indicate this is a Bank 2 O2 sensor problem and that it is failing to switch and adjust for the fuel mix. But as you can see, many defects can lead up to this O2 sensor Code 1150.

I would try to use a spray bottle of water and go around the Intake manifold and spray the water while the engine is running. An intake leak will draw water into the engine and change RPM.

If no success then try changing the O2 bank 2 sensor. You may need to wipe the computer and clear the Code. H40 DTCs P1131, P1132, P1151 AND P1152: UPSTREAM HO2S NOT SWITCHING. DTC P1130: FUEL SYSTEM NOT SWITCHING AT FUEL TRIM (RICH OR LEAN)
Diagnostic Trouble Codes (DTCs) P1131 bank 1 (Cylinder 1) and P1151 bank 2 indicate the fuel/air ratio is correcting rich for an overly lean condition. The HO2S voltage is less than 0.45 volt. DTCs P1132 bank 1 (Cylinder 1) and P1152 bank 2 indicate the fuel/air ratio is correcting lean for an overly rich condition. The HO2S voltage is greater than 0.45 volt.
DTC P1130 and P1150 indicate the fuel control system has reached maximum compensation for a lean or rich condition and the HO2S is not switching.
DTC/HO2S Reference List
•HO2S-11 = DTCs P1131, P1132 and P1130
•HO2S-21 = DTCs P1151, P1152 and P1150
Possible causes:
Fuel system
•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
Induction system
•Air leaks after the MAF.
•Vacuum leaks (vacuum lines and gaskets).
•Restricted air inlet.
•PCV system.
•Improperly seated engine oil dipstick.
EGR System
•Leaking gasket.
•Stuck open EGR valve.
•Leaking diaphragm.
Base engine
•Oil overfill.
•Cam timing.
•Cylinder compression.
•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. )

I don't care how handy you are , that's not going to help you unless you have knowledge of OBD 2 engine management system for your vehicle . Plus having diagnostic test equipment , scan tool to view engine sensor data ., an knowing how to do automotive electrical circuit testing.
Po171 Could be just an O2 sensor problem ,looking at scan data for bank 1 sensor 1 for proper switching , could be a easy find for a trained Tech . You on the other hand could spend hundreds an still not fix the problem .

P0171 - System to Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. For lean and rich DTCs:

• 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 HO2Ss.

P1130 - Lack of HO2S-11 Switch, Fuel Trim at Limit The HEGO Sensor is monitored for switching. The test fails when the HO2S fails to switch due to circuit or fuel at or exceeding a calibrated limit.

• Electrical:
  • Short to VPWR in harness or HO2S
  • Water in 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)

A fuel control HO2S PID switching across 0.45 volt from 0.2 to 0.9 volt indicates a normal switching HO2S. P1131 - Lack of HO2S-11 Switch, Sensor Indicates Lean A HEGO sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time. See Possible Causes for DTC P1130
P1151 - Lack of HO2S-21 Switch, Sensor Indicates Lean A HEGO sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when fuel control system no longer detects switching for a calibrated amount of time. See Possible Causes for DTC P1130 006 O2 Sensor Signal Analysis

CODE PO151 - HO2S - 21 BANK 2 SENSOR 1 CIRCUIT LOW INPUT. CODE PO153- HO2S BANK 2 SENSOR 1 CIRCUIT SLOW RESPONSE. CODE P1151 - LACK OF HO2S - 21 SWITCHING HO2S SIGNAL LOW INPUT. POSSIBLE CAUSES TO YOUR PROBLEM AIR INTAKE SYSTEM LEAKING VACUUM HOSES LEAKING OR DAMAGED.AIR LEAKS LOCATED AFTER THE MAF SENSOR MOUNTING LOCATION OR IN THE PCV SYSTEM. YOU COULD HAVE BASE MECHANICAL FAULT LIKE LOW CYLINDER COMPRESSION , VALVE TIMING OFF.HO2S CIRCUITS WET OR OILY CORRODED OR POOR TERMINAL CONTACT. HO2S SIGNAL CIRCUIT OPEN SHORTED TO GROUND SHORTED TO POWER OR THE SENSOR HAS FAILED. LOW FUEL PRESSURE OR VECHICLE DRIVEN UNTIL IT WAS OUT OF FUEL. BEFORE REPLACING PCM CHECK ALL VACUUM HOSES ON INTAKE MANIFOLD. REPLACE FUEL FILTER. CHECK YOUR SPARK PLUGS. IF SPARK PLUGS OIL COATED PROBLEM IN THE ENGINE ITSELF. YOU HAVE WORN PISTON RINGS, WORN VALVE GUIDES AND WORN VALVE SEALS. IF PCM WAS BAD YOU WOULD HAVE FLASHING CHECK ENGINE LIGHT CAR WOULD RUN POORLY.YOU WILL HAVE FAULT PCM CODE IF PCM FAILED. YOUR PROBLEM IN HO2S SENSORS AND THE ENGINE AIR FUEL MIXTURE.

P1131 Lack of HO2S-11 Switch ,Sensor Lean
P1151-Lack of HO2S-21 Switch ,Sensor Lean
PO171- System to Lean (Bank 1)
PO174-Systen to Lean (Bank 2)

Fuel Filter -Plugged
Low Fuel Pressure
Evap System -Leaks
Leaks - in ducting,air filter to throttle
PCV -Leaks
Exhaust System -Leaks
O2 Sensors-worn out

P1131-- Lack of HO2S-11 Switch (lean)
P1151--Lack of HO2S-12 Switch (lean)

There are at least 26 possible causes in the
Diagnostic Trouble Code Chart

That isn't going to be a driveway job,
your going to resolve

CODE P1151 LACK OF HO2S 21 SWITCHING HO2S SIGNAL LOW INPUT.POSSIBLE CAUSE LOW FUEL PRESSURE.INJECTORS STOPPED UP.FAULTY HO2S SENSOR LOOK FOR INTAKE AND EXHAUST LEAKS.LOOK FOR AIR LEAKS LOCATED AFTER THE MAF SENSOR MOUNTING LOCATION OR IN THE PCV SYSTEM.