JEBSR5

90 4Runner V6 3VZE 4WD 5 speed.
Keep getting code 21, strange part is that it does it only once in awhile. Oh, maybe once in two weeks, but check engine light never stays on. Goes out after maybe 30 seconds, but leaves code 21. Checked resistance of O2 sensor and it reads 7.9 OHM's. That's with exhaust and sensor cold. Is this bad? If so, any recommendations on replacement brand. Cheapest around here is $68 and highest is $140+. By the way, gas milage dropped from 19.6 to 17. Only choices I have around here is Advanced Auto, Autozoned and NAPPA. Have to drive long, long way for Toyota dealer, unless I go to local stealership (I mean that literally).

Toysrme

Sensor is dead. Diag. trouble code 21 is for the left bank main oxygen sensor circuit.
If the 3vz-e uses a 1-wire sensor, you can buy generic splice in Bosch unit for $30-35.

I've got two in my car. Splicing isn't a big deal, it's just one wire.

JEBSR5

Mine is a 4 wire. That Bosch unit mentioned here is $68.

runethechamp

You could check out this one: http://personal.utulsa.edu/~nathan-b...01heatedox.pdf

Seems like your O2 sensor resistance is too high.

JEBSR5

Thanks for the schematic. Wow, 7.9 is way above the tolerance level. I'll try the heated check to be sure, since the prices here are really high. Did find a Denso for $68.99 on web. Still checking for prices on web, useless to look here local. Denso's write up on their sensor seems pretty good, but you know what they say, looks good on paper.

Thanks again.

Techsus

1991 XtraCab Deluxe Pickup I4 2x4 5-speed 22R-E

Haven't had to bother you for a looong time, until CEL came on today. Original owner of this '91 baby so I know HO2S is original! (Check Engine Light has NEVER lit up in 24 years, Go Yota.)
Please be patient, not a trained mechanic but enjoy DIY. Reading Chilton's, watching several YouTube videos & researching Toyota forums-- "still" can't find this sensor (forgive my ignorance). Anyone patient enough to give a DIY'er blow-by-blow of where to FIND this puppy? And...how to proceed to clear CEL?
Also, I appreciate your suggesting "where to begin" to repair Code 21. I.e., just install a new one? If 89465-39226 is correct part # it's $131.49 + shipping. Wow.
Thanks a ton!