oxygen sensor replacement

There are two oxygen sensors. One is upstream from the catalytic converter, and the other is downstream.

You may want to consider using the correct oxygen sensor which is equipped with the correct wiring harness connector. If you don't see the wiring harness connector, you'll probably have to access it from inside the vehicle.

I believe that the oxygen sensor will have four wires (two for the sensor and two for the heater), so if you use a generic sensor then you'll have to figure out which wire goes where.

 

I was totally unable to figure out how to get the front O2 sensor out of my car. Is their an access panel under the rug?

 

I don't have the 2001 repair manual any more, but I do recall that it is necessary to remove some passenger cabin trim to access the front oxygen sensor wiring harness connector. It might be hidden under the center console.

You might consult techinfo.toyota.com to obtain the specifics. Good luck.

 

My problem was not with the wiring. I never got that far. The sensor itself was on the inside of a crook in the exhaust pipe in such a way that I couldn't get any sort of wrench on it. But if the wiring goes through the floor, it occurred to me that maybe there was access through a plate in the floor.

Not important really, since I paid a local shop to do it, and I won't be changing it again for quite a while.

 

Yes. Why do you think either O2 sensor needs to be replaced?

The usual way to determine that an O2 sensor needs to be replaced is that you retrieve a DTC logged by the engine ECU which is related to the sensor. The way to confirm that the O2 sensor is bad is to observe the voltage waveform produced by the sensor after it has reached operating temperature. The first O2 sensor should produce rapid voltage changes which results from the engine air/fuel ratio swinging back and forth between lean and rich. This shows that the engine ECU is controlling the air/fuel ratio in closed-loop operation.

If you have driveability issues which relate to the oxygen sensors, then the first oxygen sensor should be replaced.

The purpose of the second oxygen sensor is to help the engine ECU determine whether the catalytic converter is functional or not. It has no impact on engine performance.

You would normally expect the second oxygen sensor to show more gradual voltage changes compared to the first. This demonstrates that the catalytic converter is functioning. If both oxygen sensors produce a similar waveform then the engine ECU will conclude that the catalytic converter is not performing.

 

If I correctly understood what Patrick said, I guess what you are seeing could mean that something is wrong with one of the oxygen sensors, or it could mean both sensors are fine and they are telling the truth about your catalytic converter as they were intended to do.

I guess the next diagnostic work that needs to be done is to separate those possibilities.

-Chap

 

I know the OP had the work done already, but this may help others.

After failing to manage the replacement myself, I had a local indy shop do it for me.

They told me the Upstream sensor replacement required them to remove the wiper cowl for access.

The downstream is much more manageable. Ramp the car for the sensor, and the plug is under the passenger carpeting.

 

I am going through this whole scenario. Check Engine light with P0171 Bank 1 lean. Replaced Catalytic converter. Check engine light with same code. Tests indicated that 1st O2 was bad. Replaced. Check Engine llight with same code. Tests showed that ECM was not activating the O2 Heater. Replaced the ECM with one from another car. Worked better but not within specs. Ordered a used ECM. Car worked fine for a day and check engine light returned with P0171. Additional tests show that the ECM is not sending any signal to the second O2. I am trying to contact the place where I bought the ECM. XVipers Inc. Not responding to e-mail and voice messages. Anyone here had any experience with XVipers Inc.?

 

The guy that runs Xvipers is a liar and a thief. If you get what you want and it works, you may think he's a decent guy, but a quick perusal through his ebay feedback shows that sometimes he fails to send the part, or sends the wrong part, and does not make any attempt to make it good. He blocks your phone number and refuses to respond in any way. Forget about expecting him to cover a warrantee on a bad part.

 

If you have a Gen 1, make sure the mechanical valve in front of the cat is opening and closing easily. You can hand brake vacuum pump and manually operate the diaphram / linkage. They rust shut in anywhere with salt.

 

You got me on that - can you please elaborate.
Cheers

 

The concept is to use a hand-operated vacuum pump, attach that via a rubber hose to the diaphragm, and see whether the valve will move when you apply vacuum.

 

Oh, OK. Thanks Patrick

 

I am a new here. So please be kind to me. Ok I spent most the day locating the sensors. But I ran into major challenge. The upstream sensor has a cowling that prevented me any access to remove the sensor. What is the best way to access the sensor to remove and install the new sensor?

Also can you be specific where under the carpet is the connector for the downstream sensor.