Totally agree,
Geeez, you can get a pre cat o2 for 89.99 at ......what parts store does everyone recomendhere again?? TRD ....something something....
I just bought a "DENSO" "1st time fit" 02 sensor for my 99' and I did notice a difference as well in MPG. I just did the Pre cat O2 sensor to save some cash and i worked....I think the (after CATTY) o2 sensor is good for much longer...I hope so, because Idon't tink I'll be able to get the bolts off....

HERE IT IS :
and the store is..........
UNDERDOG RACING DEVELOPMENT (or URD)
(for a DENSO" "1st time fit" 02 sensor)
I paid 79.99 for a PRE CAT O2 sensor....an a little word to the wise, Also replace the o2 bolts...as I had a real Bi 'ach of a time trying to remove the bolts from my o2 sensor....
a 2 hour job!!!! Midwest road salt...hope that helps out a "brother in need"

FYI some say these o2 sensors are 75,000 Max sensors....AND with outr engines THe sensors can go out and your fuel economy can suffer a long time even without a Check Engine Light (cel) Also check withyour V.I.N as I think some "California versions" of the 3.4 call it a AIR /Fuel sensor/A/F Sensor....?
Good luck

 

I agree. When a customer asks me about replacing an O2 sensor I just tell them up front; Yes you can replace them at certain mileage intervals, but personally I'd just use a scan tool and check the pre cat and post cat readings to see if they are both working properly instead of shelling out $80+ for a brand new one. Should you decide to replace them PLEASE do not go out and buy the universal O2 sensors. If wired properly then it's fine, but if not you go through the headache of taking the sensor off and trying to reconnect the wires and etc. when you would've been better off doing the same job once with a brand new sensor with a connector.

 

I have a rear OEM o2 sensor for sale if interested

$50 shipped.