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Oxygen Sensors - FAQ

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#1 · (Edited)
WHAT ARE THEY AND WHAT DO THEY DO?
OXYGEN (O2)SENSORS: Diagnose and Replace

WHY DO I CARE?
Typical scenario is that you get the odious CEL.

Instead of posting, "oh noz I gotz a CEL" (or for you Westcoasters "oh noes i has a CEL"), you run to the auto part store, borrow the OBD reader and get your code read. You write it down, then search here with that code.

NOTE: Your error code may not be O2 related.

WHAT IS THIS OBD YOU SPEAK OF, TELL ME MORE?
What Is OBD?

WHERE IS THE OBD PORT ON THE IS300?
Directly under the steering wheel, you will feel a port with a cap on it behind the knee panel. It is the white thing in this pic below.



WHERE ARE THE ACTUAL O2 SENSORS LOCATED ON THE IS300?
The IS300 has 4 oxygen sensors, named B1S1, B1S2, B2S1, and B2S2.

Bank 1 (B1) refers to the first bank of cylinders or 1-3 (first three as you look at it from the front) Bank 2 (B2) is the second bank of cylinders 4-6 (back cylinders closest to the fire wall).

Sensor 1 (S1) is the first sensor in the particular bank (1 or 2) in the path from the engine block and out. Sensor 2 (S2) is the next one in-line.

B1S1 should be the first one you see as you look in the engine bay. It is up high, and toward the front. The one below that is B1S2.

B2S1 is near the firewall. The one under the seat (under the car) on the Y-pipe is B2S2.

Sensor 1s are "pre-cat", and check A/F mixture, Sensor 2s are "post-cat" and check catalytic operating efficiency.






Thanks to digger08 for the below pic.




WHERE CAN YOU BUY THEM?
Dealers, of course. Your local auto part store sells generic ones, but most likely they will need to be spliced in. Most people swear by Denso since those are OEM. Generic ones are cheaper, but of unknown quality, and do not just "plug" in.

Here are some online sites, you can get a Denso 02 Sensors: Denso starters, alternators, iridium plugs, fuel pumps and glow plugs, OELEXUSPARTS.com, or Sewell Lexus Parts and Accessories Online - All Genuine Lexus Original Equipment Parts. They are all around the $100-$150 neighborhood with shippine. Generics can be as much as half that amount.

WHAT ARE THE PART NUMBERS?
If somebody knows the part numbers can they post them up? I think they may have multiple numbers as well. Double check with the seller before you pull the trigger, also report back if they are right or wrong.

Here is what I have heard, these are not 100% confirmed. (* = slightly confirmed, ** = pretty much confirmed)

Bank 1 Sensor 1:
89465-53090 (2001) *
89465-53140 (2001) *
89465-53210 (02+) **

Bank 1 Sensor 2:
89465-53110 (2001) *
89465-53200 (02+) **

Bank 2 Sensor 1:
89465-53110 ?
89465-53200 ?
89465-53190 (02+) **

Bank 2 Sensor 2:
89465-53120 (01) **
89465-53190 (02+) **
89465-53150 ?

HAS ANYBODY DONE A DIY YET?
Yes you are in luck, as long as you need to fix B2S2. It will at least give you a general idea of what is involved as well when replacing an O2 sensor.

http://my.is/forums/f115/diy-p0161-o2-sensor-b2-s2-change-pics-263613/

WHAT IF I JUST GOT A HEATER CIRCUIT MALFUNCTION, DO I NEED TO REPLACE MY SENSOR?
No, you can bask in the yellow glow of your CEL and leave it alone (does not effect drive-ability), or you can do the following work-around.

http://my.is/forums/f88/how-fix-p0161-o2-sensor-heater-circuit-malfunction-b1s2-free-p0141-290038/

WHAT IS THIS 02 SIMULATOR I HEAR ABOUT?
By way of installing headers you are removing your catalytic converters to increase flow. By removing your cats, your B1S2 and B2S2 oxygen sensors will tell your ECU that something is wrong.

An 02 Simulator will give the ECU the impression that everything is A-OK with B1S2 and B2S2, and your CEL will not shine.

This can be a route to consider if you don't have headers but a B1S2 or B2S2 goes bad, as an O2 simulator is cheaper than a new O2 sensor. Remember these sensors only detect how well your cats are working, they do not effect drive-ability or performance.

http://my.is/forums/f88/how-install-o2-simulator-284733/

http://my.is/forums/f88/o2-simulators-dummies-336947/

ALRIGHT I'M READY TO CHANGE MY O2 SENSOR, WHAT DO I NEED TO DO?
Wait to your manifold is 100% cool, unclip it and hit your sensor threads with some PB Blaster. Let it work it's magic. Then use either the special 02 socket (has a slit in it) or just a normal 22mm wrench, and unscrew it.

Get your new 02 sensor, dab a little anti-seize on the threads. Make sure it is O2 safe anti-seize, you don't want to ruin your brand new sensor right away.

Screw in your new sensor and make it a little more tight than your oil drain plug, but not too tight. Then clip it in.

If you have any other tips, info, pics, or links post them up.
 
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#137 ·
i replaced the b1s2 with the bosch universal... matched up the appropriate wire colors and everything. but my check engine light is still on. reset the battery, and after 30 miles, it still came back on. need to fix to pass smog. help???
I would pull the codes again. I wouldn't be surprised if another one went bad.
 
#139 ·
Well who knows it could be a result of bad gas or even the gas cap. My suggestion is to read the code or simply reset your ECU and see if it comes back on. Anything can trigger the CEL and even if the issue went away..the computer needs reset. Stupid little light...lol
 
#141 ·
Oxygen Sensors & Cylinder / Location

For whatever reason, websites don't list sensors as B1/2 and S1/2. They list them in terms of cylinder and location. Here is the breakdown:

B1 = Cylinders 1-3
B2 = Cylinders 4-6

S1 = Front
S2 = Rear

I had my B1S2 replaced with Denso Part 234-4015 earlier month. So far so good.

I hope this helps. Cheers!
 
#147 ·
I got the placement of the sensor figured out. But just not sure if the sensor is plugged into the right part of the engine harness. there are two plugs near the front passenger side of the cylinder head. how do i know which one b1s1 plugs into and which b1s2 plugs into? When my sister owned the car, she brought it to a shop to fix this issue and they changed all the o2 sensors and exhaust mani but still coming up with o2 faults. i just swapped out the b1s1 sensor and p0135 popped up again..
 
#148 ·
Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

So you need to check the resistance and continuity in the sensor, if that is OK then check the voltage (power side) and ground path on the low side of the connection.
search for the proper procedures.

Others that have had this problem have posted threads on here, heater circuit problems seem quite common.
 
#150 ·
Ok on my 2004 the lower one, looks more grey and loose in your pic, goes to B1S1

BTW both mine are the same grey color .....both attached to the bracket on my car.

Its easy to follow this wire to the Sensor.
 
#153 ·
heater circuit malfunction

I followed your directions which were great by the way, but my problem continues. I did a code read after installing the new b1s2 oxygen sensor made by lexus and the code reads p0141. What I want to know is WHERE is the "heater circuit?" nothing more nothing less, a picture by anyone would be great. I am assuming the heater circuit is the connector attached to the oxygen sensor.

alvaro quinonez
 
#154 ·
I followed your directions which were great by the way, but my problem continues. I did a code read after installing the new b1s2 oxygen sensor made by lexus and the code reads p0141. What I want to know is WHERE is the "heater circuit?" nothing more nothing less, a picture by anyone would be great. I am assuming the heater circuit is the connector attached to the oxygen sensor.

alvaro quinonez
The heater circuit is a part of the 02 sensor. Inside of an O2 sensor is a sensor signal circuit and a heater circuit. The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The two black wires on an OEM Denso sensor are the heater wires and should read about 10-14 ohms @68*F, IIRC.

P0141 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank1, Sensor2)

Replacing the correct sensor should have solved the problem. Check to see if the connection harness is tight(by the air box) and possibly reset/clear the code by pulling the negative off the battery for a few minutes. Other than that, they either replaced the wrong sensor or the new one is bad, which they should replace free of charge.
 
#158 ·
Hello All,
I have been lurking for about a week and wanted to post on here to make sure I get the right O2 sensor and have the right location. The Code im throwing up is a P0430 Catalyst System Efficency Below Threshold (Bank 2). I have been reading on this forum and using the search function to make sure I have the right location and right sensor but want some reassurance. Is this O2 sensor it is identifying the one under the passenger area that you can plainly see and that some have removed the seat to get to it easier? I want to verify before I start taking one out and changing it. From what I have read this is the right location. I am at Densoproducts and sparkplugs.com and on eBay and want to verify im looking at the right o2 sensor too. Since the dealer wants 190 for this sensor, i'm going to try and change it for cheaper :)
Densoproducts.com shows Front cylinders 4-6, front upper cylinders 1-3 , rear cylinders 1-3 and rear cylinders 4-6. It doesnt mention the one after the cat (downstream I guess) . This is the one im looking at on ebay New Rear Bosch O2 Oxygen Sensor Lexus IS300 2002 2001 Parts Auto Car | eBay
I bought the car a week and a half ago and have unplugged the batt 2 times and cleared the code twice. The same code keeps popping up. I ran seafoam in the tank as well. I test drove the car 3 times and it never came on. I got 91 gas in it (previous was putting 87 in mostly and occasional 91) and about 20 miles later the light came on.
Thanks again to the community for your help
BTW its a 2001 Lexus IS300 with 203k miles. (high miles I know, but I had faith in it, no leaks no burning)
 
#159 · (Edited)
Yes, P0430 is bank 2 sensor 2 is a cat efficiency code. It can be caused by a cat going bad, an exhaust leak, or bad o2 sensor. It is easier to check for leaks and replace the O2 sensor, even though the sensor can be tested with a voltmeter to verify it's .2 to .9 volt fluctuation. You don't nessesarily have to remove the front seat. I know some members have moved the seat forward and up all the way and had enough room to pull the old sensor wiring out and fish the new sensors wiring in. It is located at the Y pipe, directly below the seat. If you do remove the seat, make sure to disconnect the battery and wait a few minutes before doing any work, this is to prevent the airbags from deploying when the seat harnesses are disconnected. IMO, I would go with an OEM Denso replacement, but Bosch is fine and that link looks like the correct sensor. This image here shows all the o2 sensor locations and the part numbers to replace them with.

Http://img522.imageshack.us/img522/8813/o2diagram16.jpg
 
#161 ·
Perfect, Thank you Jasonm444. I may just go ahead and purchase the Denso. If I get the one with the plug already on it, I should still be able to just move the seat forward right and disconnect the current one and connect the other? I don't really wanna deal with air bag change of deployment.
 
#162 ·
Yes, I've heard but not actually done myself, that you can move the seat all the way forward and high as it can go. You can cut the old sensor's wires and use them to fish the new ones into the car. Just tape the new sensor's wires onto the old wiring. Removal of the seat is really no big deal, basically 4 bolts and a few harnesses, but the battery does have to be disconnected and a there is a couple minute waiting period before disconnecting the seat harnesses. Ahh, and sorry about ya Blacksport. Our vendors can definitely help you out there as well.
 
#163 ·
I'm prolly cursing myself but, the code hasnt come back on since I cleaned the MAF and cleared the code for the o2 sensor. It usually would have come on by now. Ive put 80 miles on it and no code, usually it would throw at 20...don't know if this has anything to do with it, but the previous owner said he sometimes would hit it with 91 but usually ran 87, you think it has some gunk on it and the seafoam and normal 91 finally cleared it through?
 
#164 ·
Well, I hope for you sake it does not come back on, but since it's a heater circuit malfunction, it 95% of the time comes back. If it's not a connection, then it may be slowly going bad(internally). I would wait till 500 miles or so before you get your hopes up.
 
#168 ·
Went back on 20 miles after getting gas, just like it did the first time. Seems to come on 20 miles after getting a fresh tank of gas. I went 160 miles without the code and then filled up and it went off. Sigh, oh well. I'll get the 02 on my next paycheck. Getting the tie rods replaced and plugs changed with this paycheck lol
 
#169 ·
sorry to hear. It's worth it to just change the O2, as you mentioned, or test it if you have a voltmeter and are the hands on type. I would also check for any exhaust leaks. If the code comes back after a new O2 or if the sensor voltage fluctuation tests ok, then you may have a cat issue.
 
#170 ·
I've been searching around the forums and just want to make sure I have this right. I bought my IS300 a couple of months back and had a CEL. When I checked all 4 o2's were bad. I bought aftermarket headers and also bought the Token Solutions o2 delete. I reset the codes and a couple of miles later I got the CEL. I put the computer on and got B1S1 and B2S1. My question is this, if I buy those two o2's and put them in will the CEL go off or it won't because of the headers? Thank you guys.
 
#171 ·
You need the S1's, both of them, to control the fuel mixture, with or without headers. The O2 delete is for the S2's
UNLESS you have a replacement fuel control solution, stand alone computer etc ....
 
#174 ·
Here is my problem:

Code P0038: Oxygen sensor heat control circuit high voltage B1S2

My setup is Mazzuri headers, SRT intake, Token Solutions O2 Delete

I just replaced my old O2 simulator with the Token Solutions O2 Delete. I've probably only driven ~750 miles since, max, and I did rewire the ECU back to stock when I removed the O2 sim. I have had emissions checked within that time with no issues.

So, the question is, what could have gone wrong? Loose connection in rewire of ECU? An issue with the O2 delete (which I honestly do not completely understand how it works)? Safe to drive?
 
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