O2 sensor(s) replace 1 or both upstream?

[Chris45342]

'98 3.8 V-6. 166,500 miles. Got a P1131 and also a P1132 code to set. Did wires and plugs which it needed anyway due to P0302 #2 cylinder misfire (only happened once) and they looked sad. I think the heater is out on the Bank 1 Passenger side oxygen sensor. Was wanting to throw a new one anyways to get rid of the MIL light. The question I have tried everywhere to research is "Is it best I change both upstream O2 sensors even though I have no code for the other bank?" Half say yes, half say no. Also what about the one after the cat? I can go either way. I'd think they would perform better if matched and same age. Unknown how old they are but if they looked anything like the spark plugs and transmission pan, I'd do both upstream at least. Thinking a couple NTK 22016 (not those universal kind) sensors from an advertiser on here. Bought this car not too long ago, been neglected but pouring lots of love and needed parts and services in.

 

[wmburns]

Don't waste $$ replacing the rear O2 sesnsors unless they are confirmed bad. They only monitor the how the cats are working. If your research is indicating that the rear O2 sensors should be replaced as a matter of PM, then question the experitse of that advice.

Replace both if over 100k miles.

If $$ is not an issue, replace both unless you are sure the other is good. This gives the advantage of working from known good O2 sensors.

OBTW, this list of possible causes is quite long.

>>
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)

 

[Chris45342]

Thank you. I'll get both upstream sensors and leave the downstream alone. I'll also check the fuel pressure and probably get a fuel filter also. They say those should be changed at 12,000 miles. Just trying to get up to par before we move to an emissions testing area in a new state.