DIY O2 Sensor Change

[Rich L]

Difficulty: 2 out of 5
Time: 30 minutes for the front O2 sensor and 45 minutes for the back sensor. Throw this time estimate out the window if a sensor is seized.

Tools you will need:
O2 deep socket
22mm deep socket with breaker bar or 22mm box wrench
10mm socket
3/8" drive ratchet
Wire cutters
PB Blaster
[Optional] Torch




Parts you will need:
Front O2 sensor, Toyota P/N 89465-12380 or Denso 234-2003
Back O2 sensor, Toyota P/N 89465-12390 or Denso 234-4061

My local Toyota dealer wanted about $375 for the sensors. I got the Denso units for about $100 from RockAuto.

The sensors looked identical but the wire shielding was much more robust on the Toyota unit then on the Denso part. The shield on the rear sensor is a full-length rubber on the Toyota unit. The shield only covers about 3" of the 6" of exposed wiring on the Denso unit. The harnesses fit perfectly on the Denso units.

Disclaimer:
The O2 sensors can be seized in your exhaust. Be cautious to not round off the head on the sensor. IMHO, you can always pay an independent mechanic a few bucks to loosen a seized sensor.


Step 1:
Spray PB Blaster on the base of the O2 sensor(s) at least one day before attempting this process. Drive car and re-spray with PB Blaster. The more times sprayed, the better.

Step 2:
Make sure the engine and exhaust is cool. Disconnect the negative battery terminal.

Step 3: Front O2 sensor
The front O2 sensor is located in the front of the car below the exhaust manifold. Find it and follow the wiring to the wiring harness. Unplug the wiring harness by pressing the tab on one side and pulling apart.




Step 4:
Remove the plastic shroud on the passenger side of the vehicle. There are six (6) 10mm bolts. Note: this step can be skipped if you wrench from the top of the engine and not the bottom. I have skinned my knuckles enough and prefer to "pull" and not "push" a seized bolt. This step is necessary to "pull" the wrench.

Step 5:
Slip the box wrench through the wiring and fix onto the O2 sensor. Alternatively, cut the wire at the end of the sensor and use the deep socket and breaker bar. I do not recommend using the O2 sensor socket because it will deform under stress and may round off the sensor.

Wrench the crap out of the sensor. I laid on the ground and used my leg to push the box wrench (not a good idea with a socket because it can rotate and ruin the sensor head). As needed, heat the exhaust pipe (not the sensor) with a torch then wrench on the sensor. My guess is it took around 200-300 ft/lbs to get it to come loose.



Step 6:
Coat the threads of the new sensor with high-temperature anti-seize compound. It was included in the box with my Denso sensors. It may already be on the Toyota unit.



Step 7:
Hand tighten the new sensor into the exhaust bung. Use the O2 sensor socket to tighten down the new sensor. I could not find the correct torque specs so I tightened it enough that the sensor would not work its way out (probably 30-40 ft/lbs). Plug in the wiring harness ensuring the wire will not hit the fan or get in the way.

Step 8: Back O2 sensor
Lift the front end of the car via ramps, lift, or jack-stands. You will be underneath the car and applying lots of torque. Make sure you properly support the car so it will not fall on you.

Step 9:
Pull the carpet out from underneath the passenger side center console as shown in the picture. No reason to remove the seat or center console (as I did trying to find the wiring). As you can see the O2 wiring comes through a hole in the chassis located approximately 4" in front of the shifting lever.

Disconnect the wiring harness. Push the rubber plug and wiring harness through the chassis or clip the wiring at the sensor.



Step 10:
Repeat step 5 for the back O2 sensor. This one was extremely tight and took all my "leg pressing" strength. I was very close slowly dropping the vehicle on the wrench and letting the car's weight turn the wrench.

Step 11:
Apply anti-seize to the threads and feed the new sensor through the hole in the chassis. Do not seat the rubber grommet yet. Hand tighten the sensor then use the O2 socket to tighten. I had a helper rotate the wiring inside the car as I turned the sensor.

Step 12:
Seat the rubber grommet in the chassis and connect the wiring harness. Push the carpet back under the console.

Step 13:
Reconnect the negative battery terminal. Double check all connections.

[speedy25]

99% of the time the sensor IS seized in the fitting. An acetylene torch is the easy way to get them free. If you dont have that moving it a bit and working penetrant in is the next best thing. Tighten and loosen to work it in to the threads.

I still have yet to figure out why in the world they make the sensor removal tool in 3/8 drive. Never is there enough torque put to a 3/8 drive that will make these sensors come out.

-SP

[96coroll]

Is there any way to test an old O2 sensor?

[Rich L]

Is there any way to test an old O2 sensor?

You have to warm up the car and monitor the voltage of the sensor. The voltage should fluctuate appropriately with applied throttle. Out of range fluctuation or minimal fluctuation may be a sign of a failing/failed sensor.

In my case, I was getting a P0420 CEL (cat low-efficiency). The post-cat O2 sensor was step 2 of 3 (check for exhaust leak, replace rear O2 sensor, then replace cat). The front sensor was $35 and seemed like a no-duh at this point. Both sensors were 16 years old and had 230k miles on them.

[speedy25]

The sensor has a millivolt output. Basically id you have output and it fluctuates with engine speed and load its good. I have had a few cars where I got a CEL for O2 sensor and a good wire brushing off all the deposits restored it and the code didnt come back.

-SP

[96coroll]

I will check the front one on my car i think it was replaced maybe 2 years ago. The one post cat i think is original though with 219km, maybe i'll just replace that one.

I grabbed an O2 sensor off another car(same one) i'm assuming from your replies there is no way to bench test the sensor?


Thanks for the help

[Rich L]

I grabbed an O2 sensor off another car(same one) i'm assuming from your replies there is no way to bench test the sensor?

Yes, you can bench test it out of the car. I have never personally gone through the procedure before, so the steps are vague for me. IIRC, you have to apply 12V to the terminals, heat the sensor with a torch, and monitor the voltage. I am not quite sure exactly what stimuli must be applied to get the voltage to vary (i.e. how to simulate different oxygen levels). Perhaps take the torch off and see that the voltage changes (?).

The downstream O2 sensor is present to monitor the catalytic converter. I have heard on some cars, it is used to attempt to determine the degradation of the front sensor. Not sure if the 7th gen Corollas do this. Personally, I would leave it alone unless you are getting a CEL or suspect a problem. That's just me being lazy though...

[Rich L]

O2 sensor has been in for 300 miles now and now catalytic converter low-efficiency CEL, yet. Seemed to solve my problem.

As a side-note, my mileage has remained unchanged after the O2 sensor change. Many mention a 10-20% decrease in mileage as the O2 sensors die. I didn't see any change.

[Corolla Sound]

When you were replacing the rear o2 sensor, how difficult was it to slip the carpet back under the center console into position? I tried playing with it today but the plastic center console (front part, I loosened the back part off) is really tight and pinching the carpet. Im worried I wont be able to get the carpet back into position..

Is there a way to loosen the front part of the center console? Is it held in by clips?

[Rich L]

Is there a way to loosen the front part of the center console? Is it held in by clips?

Interesting, mine was very easy to pull out and push back in. The back portion of carpet had a piece of velcro spanning the drivers side of the car to the passenger side. I believe the velcro is sewn on the driver-side carpet.

I suspect, but am not positive, the front portion of the console has a similar piece of velcro. Anybody able to chime in?