O2 Sensor - Bank 1 Sensor 1 - Replacement

[is200 Newbie]

O2 sensor replacement

Check VSC / traction / warning and engine lights came on recently. It started as an intermittent fault, they would light up on the way to work and go off on way home - it happened for 3 days until the lights came on permanently.

I had no choice to drive it - I bought an ODBII reader and it reported back on Bank 1 Sensor 1 failure.

I ordered two new sensors - Denso 234-9051 from the USA and they came this morning

I am replacing both sensor 1's (Bank 1 and 2) Drivers and Passenger side as it makes sense as they have been in the car for the same length of time and while I am doing one I will do the other. Bank 1, Sensor 1 is on the drivers side / Bank 1, Sensor 1 is on the passenger side. Both are accessible from the engine bay.

I replaced Bank 1, Sensor 1 tonight as this was the one reporting a failure. It took 15 mins (if that). Firstly I removed the drivers side engine cover

Next, to get to the sensor easier, loosen and remove the fuse box shown in the picture below using a 10mm socket

Do not remove from the car - just loosen - there is one 10mm bolt and one 10mm nut to take out - lift the fuse box out of the way as per the picture below

You can now see the sensor and its also easier to remove.

To remove, I used a 22mm 7/8 socket - open ended sensor socket - place this (or whatever you are using) over the sensor nut and loosen only - you may need some WD40 and a SMALL tap on the socket from a hammer to encourage it to move at first - don't take it off at this point

First remove the sensor wire socket from the cars connecting plug - you will see from the new sensor you would have bought before doing this that there is a small securing lug on one side of the plug.

Picture below is of the sensor plug still attached to the cars socket - a bit obscured

To remove this you need to press down on a tab to the rear of the plug on the car which can be found on the side of the plug facing the bulkhead. While pressing on the tab gently pull the wire and the plug will come out of the socket. In taking the fuse box out of the way there is enough room to get both your hands into the sensor area. Once this is off I secured the wire with a bit of tape to an upper hose so I would not lose it into the depths of the car if I dropped it when the socket come off - I think it would drop through the bottom of the car but just in case it didn't I secured the wire. Next, remove the sensor itself. Doing it this way it will not twist the wire up as there are quite a few turns required to remove the sensor.

With the sensor removed - (dead one shown below)

Replace with the new one. Place the anti sieze compound on the threads of the new one before inserting it into its location. Put the sensor in first and then once secured fully, plug it into the cars socket.

Replace the fuse box and engine cover.

Job Done - re-connect the Battery and you should have no more nasty lights on the dash. Reset the windows once you are happy with the job.

I checked the error had gone by re-scanning the car with the OBD reader again.

Noticeable differences. There are obviously a few - quieter running / revs are way down / too early to report on fuel consumption / car is now not lumpy when idling.

Next job would be to do Bank 2, Sensor 1 - that's a weekend job as its getting a bit dark now.

Pictures below of before and after on engine report

Before

After

[is200 Newbie]

I cant seem to match the pictures up with the text so have indicated the picture number within the text.

I will be doing the second sensor at the weekend if the weather holds and will post the how to for that one then.

[ColinBarber]

I've edited your post to put the pictures inline.

Good job there, hopefully the other sensor will be as easy.

[normski2]

Noobie

Please copy your post and stick it in here

http://www.lexusownersclub.co.uk/forum/tutorials/category/6-lexus-is-2005-onwards/

Most definitely where this belongs, for all to find with ease. You'll see your slide pins guide there!

[james250]

Great writeup.

Quick question, is the following correct:

Bank 1, Sensor 1 = Air/Fuel Ratio Sensor

Bank 1, Sensor 2 = Heated O2 Sensor

Bank 2, Sensor 1 = Air/Fuel Ratio Sensor

Bank 2, Sensor 2 = Heated O2 Sensor

So, which ones did you replace? Did you replace B1,S1 and B2,S1, if so that's both the Air/Fuel Ratio Sensors and not the actual O2 sensors? From the part number it looks like it is the Air Fuel Ratio sensor and since you posted pic of one sensor, I am assuming its the same sensor for B1,S1 and B2,S1, is that correct?

[ColinBarber]

yes you are correct. The upstream sensors are air/fuel ratio sensors (wideband O2 sensors) and the downstream sensors are standard O2 sensors. The downstream sensor are only used to try and determine if the cats are working correctly. The upstream sensors are the ones that determine the air/fuel mixture.

This tutorial is for replacing the upstream sensors

[is200 Newbie]

James - as Colin said ....

The sensor I changed was the B1,S1 - Air fuel ratio sensor located in the engine bay - the sensor before the cat (drivers side)

The sensor I will be doing tomorrow will be B2,S1 - Air fuel ratio sensor located in the engine bay - the sensor before the cat (passenger side)

There are, as you stated above, 4 sensors in total. I have purchased two of the 234-9051 Denso sensors. The one I have replaced yesterday was fine. I have had a look at the other one and the wire length looks ok as well.

Will post another how to after the second one is done.

Both sensors, including postage cost me 246 usd - I didn't get hammered for duty (lucky break)

[is200 Newbie]

I have replaced Bank 2, Sensor 1 now and the guide on how to do this is in the How to Guides section for IS250

[Exdee]

Thank you so much for both your guides. I replaced both sensors today.

I've got gorilla hands so it took me quite a while to do this but the sense of achievement is great.

[toffee_pie]

what milage on yours? mine is on 60k think this is my next job

[Exdee]

Mine is 84K.

I also did water decarbonization yesterday. Something I've been reading into and wanted to do for a long time. Sprayed about half a liter of water into the engine via the air intake using a spray bottle.

I did this before I did the oxygen sensors and the result was quite dramatic. Not only did the engine become a lot more quiet, the acceleration felt very smooth and linear.

The oxygen sensors were a cherry on top.

Overall, It has made a significant difference to the way the car sounds and drives.

[is200 Newbie]

I have heard about this, considered "old school" in the states but with excellent results but it must take a leap of faith to actually do it yourself, spraying water into your engine goes against all logical thinking ... but I guess its just a fine mist (a bit like condensation that will burn off naturally) - supposed to be better at removing carbon deposits than any chemical cleaner....

Where you have said you have sprayed it into the air intake have you removed the plastic around the intake and sprayed directly down into the metal air intake body?

I have used Air Intake / Carb Cleaner (aerosol) in the past as I was recommended it by a friend (smelt a bit like kerosene) I could not tell if that actually made any difference but it did light up the dash board lights but as it evaporated they went off.

Did you have the car at high revs when doing this? and experience any issues?

[Exdee]

I disconnected the intake tubing right after the air flow sensor and before the throttle body as show in this video. I had the car around 2.5 RPM when I did this initially but then dropped it to 1.5 as I got confident that the engine did not mind the little drink and the fact that I was spraying in very small quantities.

I am not sure about lights on the dash as mine were on already due to a failed oxygen sensor. One thing to bear in mind is that the car dies on low rpm without the air flow sensor connected so every thing needs to be connected before easing off the accelerator.

I have driven 50 miles since and no issues so far. I will probably do it again some other time. Rain interrupted so I didn't get a chance to do it for long.

[ahmed24]

Great write-up IS200 Newbie. I might go ahead and change my two upstream sensors as preventative measures. Mine are still on originals since 2006, not having any issues with them or bad mpg. I think it's worth getting a new set.

[is200 Newbie]

After I had changed both I did notice a difference in response and also MPG - placebo affect? probably.

I read that its recommended they are changed between 70 and 100k whether that's a preventative measure I don't know and whether its on the Lexus service schedule I don't know. Its an easy job - doing it yourself which going by the work you have already done on your car, you will be more than capable in changing them out. Cost wise, around £150-160 for the parts if you fit yourself. Lexus to supply and fit = over 600 £ !.

[ColinBarber]

Replacement isn't on the service schedule but they do seem to fail around 80-100k miles and even before failure they are probably working sub-optimal so replacing at 70k isn't such a bad idea but obviously there are exceptions and people can get 150k miles from a sensor.

[ahmed24]

Replacement isn't on the service schedule but that do seem to fail around 80-100k miles and even before failure they are probably working sub-optimal so replacing at 70k isn't such a bad idea but obviously there are exceptions and people can get 150k miles from a sensor.

I guess my upstream sensors are way overdue a change now then :)

Thanks IS200 Newbie for the guide.

[agent_dess]

Anytips for ppl with goriila hands such as myself? I did attempt to change them once, but lack of space and my hand size prevented it, I have since bought the 22mm sensor socket and got a really long torx wrench so will attempt again when I have time but any advice would be appreciated.

[is200 Newbie]

The sensor location under the side the Battery is on has limited space to get to it but if you take out the parts as shown and take your time doing it then its do-able.

There may be other parts you can remove other than the parts shown but I cant say as I managed to do it by just removing the ones shown.

The sensor will be on with thread lock so will be initially hard to loosen due should come off quite easily once freed.

[agent_dess]

The day I tried it, I went to do the one located under the intake pipe, I moved the fuse box as per ur guide but I still found very little room to work with, but will have a go again once weather improves

[agent_dess]

So I tried and failed and give up! I just couldn't unscrew the old sensor, even applied a lot of wd-40. I've been defeated :(

[is200 Newbie]

I think it was a case of using a bit of force (with small hammer taps) when mine came out - breaking the thread lock that's applied when they are first put in.

If you were closer I would give you a hand

I am due a trip up to Dundee in a few months - are you anywhere local to there?

[toffee_pie]

Noo-bie? how many o2 sensors in total are on the is250?

[ChumpusRex]

4 O2 sensors

2 pre-cat wideband sensors

2 post-cat narrowband sensors

[toffee_pie]

thats alot of o2 sensors! most cars I had before had 1.