At 107,000 miles the original O2 sensor in my 1988 SR5 4x4 pickup was tiring. The high-low voltage switching rate test covered in the shop manual gave marginal results. Since I'm about to embark on a cross-country drive, I figured a new sensor would pay for itself in better mileage very quickly.

I ordered a new Denso sensor on eBay. It arrived without a gasket. I figured that was no biggie; I reused the old one. Then my truck started setting codes (25) every time I drove over 40 mph. WTF? I didn't make the connection until I read it online. Inadequate gasket -> air leak -> O2 from outside hitting sensor -> computer enriches mixture and eventually burns out the CatCon while delivering terrible mileage. A gasket from the nearest Toyota dealer cured the problem, but they charged $15 for the part. Hopefully others will profit from this lesson and either make sure their sensor comes with a gasket, or else buy it online where it's much, much cheaper.

The other surprise was that the new sensor came without the grommet that seals the opening underneath the cab. The opening in the center of this grommet is way too small for the plastic connector shell.

I had just learned how to unlock terminal pins from connector shells while I installed a radio. I put the new skills to work with the O2 sensor cable. Got the wires/pins out of the shell, passed them through the center hole in the grommet, and put the shell back on. And so it's all good as new.

 

Can you post the link to ebay where you purchased the O2 sensor. I am getting ready to replace mine. Thanks

 

^^ Same here. I assume it was $100 or so?

 

I got my new Denso O2 sensor from rockauto.com. It came w/a gasket AND it was only $50. Btw, don't get a universal unit. Mine is not universal.

 

Thanks Tex, was it this? Not sure if yours would be the same part # as mine though.

 

Looks to be it. I got the non-Cali. version, non-universal, and for a 3.0L.

 

The eBay seller was abcmarts. I got the part in less than a week. It cost me 65 bucks or thereabouts, plus I paid my local Toyota dealer 15 more for the gasket. The new sensor was an exact replacement for the original one.