Code 21 showed up - O2?

[PabloRunner]

Hey Guys,

I've read nearly every thread out there about this issue. So far this has probably resulted in more questions that I originally had when I started this afternoon!

Driving home from work today the Check Engine light came on. I stopped in the autozone parking lot, shorted out E1 and TE1 and got code 21 to come out. O2 sensor, right?

First: I have a 1994 3.0 V6 4runner with 177k miles. I've read that 95 had an O2 sensor before and after the cat. However, when I was under the truck today for the life of me I could only find a single 02 sensor - about 6 inches upstream of the cat. Is this the only sensor on this truck??

Second: Testing the resistance of this sensor (between the 2 black wires) when cold I got 9.8ohms. Some people say this is OK, the FSM says 5-7ohms is normal. Is this sensor good or bad?

Third: I read a thread (can't find link now) that the wire harness to the sensor can melt and cause this problem. My wiring harness was just dangling near the exhaust. Could this be my problem?

 

[john690]

working on this myself. 92 3vze. changed the sensor for a bosch, no good, got a dense, no good found a broken wire in the harness and re terminated, no good, now checking ECM terminals for voltage but hard to find exact FSM. if its not the ECM it must be the wires there is no voltage at the tips. still trying. how did you go? not much around for 92's on this issue cos most guys have 2 sensors

 

[flyinhawaiian01]

Hey Guys,

I've read nearly every thread out there about this issue. So far this has probably resulted in more questions that I originally had when I started this afternoon!

Driving home from work today the Check Engine light came on. I stopped in the autozone parking lot, shorted out E1 and TE1 and got code 21 to come out. O2 sensor, right?

First: I have a 1994 3.0 V6 4runner with 177k miles. I've read that 95 had an O2 sensor before and after the cat. However, when I was under the truck today for the life of me I could only find a single 02 sensor - about 6 inches upstream of the cat. Is this the only sensor on this truck??

Second: Testing the resistance of this sensor (between the 2 black wires) when cold I got 9.8ohms. Some people say this is OK, the FSM says 5-7ohms is normal. Is this sensor good or bad?

Third: I read a thread (can't find link now) that the wire harness to the sensor can melt and cause this problem. My wiring harness was just dangling near the exhaust. Could this be my problem?

Are you getting the same resistance from the o2's plug as well as further down the wire (ie., heading towards the ecu)? I use a piercing probe for this type of work on my multimeter, and I just follow the wire up and around, testing it at the end (the ecu), just to make sure its making its way to wherever it goes to.

If you haven't found your ecu's wiring yet, google the term "3vze ecu pinout 4runner", then check to see which one is closest to your year. It should be in the middle plug of the ecu though, almost all the ecu's I've looked at for Toyota, the o2 sensor(s) are usually in the center plug.

This should tell you immediately whether the o2 wiring is good or not. I'd disconnect the ecu from the vehicle when testing inline too, as it may throw the resistance off since its connected to the ecu itself.