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P0171 + P0174 Codes Coming On After Relpacing A/f Sensors

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Hi Folks,

The story so far on my 2001 RX300: Had codes P1135 and P1155 come up(air fuel sensors) so removed the sensors checked their resistance and they were both toast so replaced with Denso DOX-0243 sensors and codes were gone.

Then I drove car for about 10 miles and CEL came on again this time with codes P0174(bank 2) and P0171(bank1).

Now before I managed to get my own OBD-II scanner I thought it was a fuel problem as the car was missing so I put some Greased Lightning fuel system cleaner in it - would this be related?

Any suggestions???

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Hi Folks,

The story so far on my 2001 RX300: Had codes P1135 and P1155 come up(air fuel sensors) so removed the sensors checked their resistance and they were both toast so replaced with Denso DOX-0243 sensors and codes were gone.

Then I drove car for about 10 miles and CEL came on again this time with codes P0174(bank 2) and P0171(bank1).

Now before I managed to get my own OBD-II scanner I thought it was a fuel problem as the car was missing so I put some Greased Lightning fuel system cleaner in it - would this be related?

Any suggestions???

UKL- Where did you get the part # for the A/F ratio sensors? I am not familiar with that part # but it's not the right # for an RX 300 w/ 1MZFE engine. Are you sure you didn't get Oxygen sensors rather than A/F ratio sensors? Very BIG difference between them.

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I saw this post on the UK site so decided to give the sensors a go.

And yes they are the air fuel sensors both sensor 1 pre cat sensors(bank 1 + bank 2).

After doing some more internet research, I found that on the U.S. lexus forums and parts sites, Denso part No 234-9009 is often mentioned as the replacement for Lexus part 89467-48011 (which is stamped on the part in my car) along with Toyota part 89467-41011 and 89467- 41021, however, again I could not find a reference to Denso part 234-9009 anywhere in the UK or Europe. What I did discover was that Denso part DOX-0243 was cited on some UK parts sites as a replacement for Toyota part 89467-41011 and 89467- 41021. In essence then DOX-0243 seems to be the Euro equivalent of 234-9009.

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The attached document describes the functions of the A/F sensors and O2 sensors. One will not replace the other. Hope it is helpful.

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I saw this post on the UK site so decided to give the sensors a go.

And yes they are the air fuel sensors both sensor 1 pre cat sensors(bank 1 + bank 2).

After doing some more internet research, I found that on the U.S. lexus forums and parts sites, Denso part No 234-9009 is often mentioned as the replacement for Lexus part 89467-48011 (which is stamped on the part in my car) along with Toyota part 89467-41011 and 89467- 41021, however, again I could not find a reference to Denso part 234-9009 anywhere in the UK or Europe. What I did discover was that Denso part DOX-0243 was cited on some UK parts sites as a replacement for Toyota part 89467-41011 and 89467- 41021. In essence then DOX-0243 seems to be the Euro equivalent of 234-9009.

I don't know UKL, but the very presence of the OX in DOX-0243 would lead me to believe that they are oxygen sensors, rather than A/F ratio sensors. I wouldn't count on the fact that "some UK parts sources" site the DOX as a replacement for the 234 because I bought 2 new sensors (Denso) that were definitely supposed to be A/F ratio sensors according to the online seller even when I e-mailed the question. I installed them and they were indeed the wrong thing. I discovered they were oxygen sensors, not A/F ratio sensors and that their listing was wrong, but I was still stuck with them because they were "electrical" and wouldn't take them back. I still say that's the 1st place I would concentrate on. I also don't know where the # 89467-41021 comes from. I believe the original A/F ratio sensors were 89467-48010 which later changed to 89467-48011 when they lengthened the wires a little. You should be able to tell by looking at them. If they are the correct ones they should look EXACTLY LIKE the ones you took out. The oxygen sensor looks very similar but the holes are different in it.

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I don't know UKL, but the very presence of the OX in DOX-0243 would lead me to believe that they are oxygen sensors, rather than A/F ratio sensors. I wouldn't count on the fact that "some UK parts sources" site the DOX as a replacement for the 234 because I bought 2 new sensors (Denso) that were definitely supposed to be A/F ratio sensors according to the online seller even when I e-mailed the question. I installed them and they were indeed the wrong thing. I discovered they were oxygen sensors, not A/F ratio sensors and that their listing was wrong, but I was still stuck with them because they were "electrical" and wouldn't take them back. I still say that's the 1st place I would concentrate on. I also don't know where the # 89467-41021 comes from. I believe the original A/F ratio sensors were 89467-48010 which later changed to 89467-48011 when they lengthened the wires a little. You should be able to tell by looking at them. If they are the correct ones they should look EXACTLY LIKE the ones you took out. The oxygen sensor looks very similar but the holes are different in it.

Correct me if I'm wrong but the air/fuel sensors ARE the O2/lambda sensors - they are one and the same thing I'm sure.

From Toyota:

Oxygen and Air/Fuel Ratio Sensors

The ECM uses an oxygen sensor to ensure the air/fuel ratio is correct for the catalytic converter.

Based on the oxygen sensor signal, the ECM will adjust the amount of fuel injected into the

intake air stream.

There are different types of oxygen sensors, but two of the more common types are:

the narrow range oxygen sensor, the oldest style, simply called the oxygen sensor.

wide range oxygen sensor, the newest style, called the air/fuel ratio (A/F) sensor.

Also used on very limited models in the early 90s, was the Titania oxygen sensor.

OBD II vehicles require two oxygen sensors: one before and one after the catalytic converter.

The oxygen sensor, OR air/fuel ratio sensor, before the catalytic converter is used by the ECM to

adjust the air/fuel ratio. This sensor in OBD II terms is referred to as sensor 1. On V-type

engines one sensor will be referred to as Bank I Sensor 1 and the other as Bank 2 Sensor 1.

The oxygen sensor after the catalytic converter is used by the ECM primarily to determine

catalytic converter efficiency. This sensor is refer-red to as sensor 2. With two catalytic

converters, one sensor will be Bank 1 Sensor 2 and the other as Bank 2 Sensor 2.

Also from: http://www.densoaftermarket.com/oxygen-sensor.php

DENSO has supplied the OE industry with quality components. DENSO continues to innovate with the latest development in oxygen sensors, known as air/fuel sensors.

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I've just done some double checking and just to clarify some terminology here air/fuel sensors are the pre-cat oxygen sensors and then there is the heated oxygen sensor(I think there is just one of these) which is post-cat.

I checked the resistance of the DOX-0243 with an ohmmeter and it gave the correct reading of 0.8 ohms so it definitely is an air/fuel sensor.

Apparantly the resistance of the "oxygen sensor"(bank 1, sensor 2) should be 11-16 ohms.

Do you know if the RX300 has 1 or 2 of these post-cat oxygen sensors BTW?

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I I didn't attach the document--sorry.

The first document describes the different functions of A/F and O2 sensors. The second document will help you troubleshoot sensors and other components on your car. Hope it helps.

A:F Sensors.pdf

SFI (SF) file.pdf

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I've just done some double checking and just to clarify some terminology here air/fuel sensors are the pre-cat oxygen sensors and then there is the heated oxygen sensor(I think there is just one of these) which is post-cat.

I checked the resistance of the DOX-0243 with an ohmmeter and it gave the correct reading of 0.8 ohms so it definitely is an air/fuel sensor.

Apparantly the resistance of the "oxygen sensor"(bank 1, sensor 2) should be 11-16 ohms.

Do you know if the RX300 has 1 or 2 of these post-cat oxygen sensors BTW?

UKL- I'm not familiar with the the term "02/lambda" sensors. Both the A/F ratio sensors (2) and the oxygen sensor (normally 1) are heated. When you checked the resistance on the 2 sensors I am assuming you tested the 2 black wires (which are the heater wires) on the A/F RS. You are correct that the Ohms of resistance should be .8 to 1.4. There is only 1 oxy. sensor which is the one after the C.C. IF the car had dual exhaust, it would have 2 C.C.'s and then would have 2 OX sensors, one after each C.C. The front sensors are definitely TECHNICALLY A/F ratio sensors and the 1 behind the C.C. is an Oxy. sensor. The front and rear sensors are often referred to as Oxygen sensors, very confusing, and incorrect.

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Well thanks for your help code58 I've now reset the fault codes P0171+P0174 and driven it 10 miles and the codes appear to be gone. :)

I reckon the greased lightning fuel cleaner had blocked a valve or something similar.

But for anybodys future information the Denso DOX-0243 air/fuel sensors do work on a mark 1 RX300. They cost me £75 each which is a big saving from dealer prices.

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Well thanks for your help code58 I've now reset the fault codes P0171+P0174 and driven it 10 miles and the codes appear to be gone. :)

I reckon the greased lightning fuel cleaner had blocked a valve or something similar.

But for anybodys future information the Denso DOX-0243 air/fuel sensors do work on a mark 1 RX300. They cost me £75 each which is a big saving from dealer prices.

Cleaners run through the intake (and even sometimes through the fuel tank) can and do affect the sensors. Most of the time temporarily and there are contaminates that can do permanent damage. A good chance that was it, since BOTH sensors were affected. (lean on BOTH banks) Glad it's fixed.

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I I didn't attach the document--sorry.

The first document describes the different functions of A/F and O2 sensors. The second document will help you troubleshoot sensors and other components on your car. Hope it helps.

JOe913: Just wanted to say thanks a million for your post. I'm having the same sort of issue(s) and feel much better equiped to tackle it...thanks again

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I I didn't attach the document--sorry.

The first document describes the different functions of A/F and O2 sensors. The second document will help you troubleshoot sensors and other components on your car. Hope it helps.

JOe913: Just wanted to say thanks a million for your post. I'm having the same sort of issue(s) and feel much better equiped to tackle it...thanks again

Hi again, just wanted to share that I tried a bottle of "STP Complete Fuel System Cleaner" worked amazing; no more engine light, car runs like new again. Highly recommend it! I also, just made sure all connections around the AF sensor and air filter were connected properly; as my issues started right after a MR. LUBE oil change, where they sold me a filter (i needed one anyways). Car is much better with the STP cleaner though. Thanks again to all for all the great info.

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