O2 sensor, front or rear?

Yes. It would be best to replace them both. Usually when one goes.......the other is not far behind. Toyota suggests the O2 sensors to be replace every 100k miles. So if you don't know when the 1st sensor was replaced, replacing it would give you a piece of mind knowing when they were all changed.

 

Gotcha. Thanks.

 

Looking up the parts on Autozone website and it looks like Denso front and rear will cost 143.99 for upstream and 89.99 aft.
Why is the NGK upstream 448.99? 300 bucks difference in price is insane.

I can't afford to do this job right now and as far as I can tell I won't harm my truck by delaying the repair. So I have time to shop around and would welcome any advice.

Thanks

 

front sensor is air fuel sensor


think of o2 sensor as a on-off switch, dumb sensor you are either in the
middle somewhere, or on one, or the other end of the range (checks for emissions compliance)

think of air fuel as a dimmer switch, more sophisticated you need to know exactly where you are (controls fuel)

I suggest denso only for replacements as denso is OEM and toyota ECU is damn fussy about every ohm and volt from these things..non-denso have a real bad rep

if you are not worried about loot then OEM only with toyota part number for these!

a/f is typically 100 bucks more than o2 sensor


your OBDII code could be exhaust leak, or bad sensor