Barnabas

Hello,
After some extensive reading about bad MPG on my car I came to the conclusion that one of the sensors needs to be replaced, specifically this one right here Denso 234-9042 It's an AF sensor for Upstream Front - However, I am having difficulties locating this upstream front and I would love some input in here. Is this for Bank 1 sensor 1 or Bank 2 sensor 1?

The car is a 2003 Lexus Es300 160,000 miles. The car is not giving me any codes, other than the fuel consumption which is about 13mpg city or 190 Miles per full tank. The car runs perfectly fine.

I was reading on some Toyota forums that this particular sensors breaks without throwing any codes and according to them this is the one in charge of the fuel and other have experienced a major increase in mpg after replacing that sensor, so I want to try it.

I already replaced the spark plugs, cleaned the injectors, changed the air filter, the MAF filter and this is why Im going to change this sensor.

Thanks for the input!

Oro

The part will go upstream of either cat on either bank. I can be bank 1 or bank 2.

This is so critical in a number of engine management calculations I would find it hard to believe it could fail w/o a code. Perhaps it could, though.

However, I would check the other causes of rapid MPG drop that don't through codes, first. Inspect the brakes for binding (simple test is to touch the wheel hub after city driving - abnormally hot = brake issue). Also check your bearing on all wheels as a bad one can cause a surprising MPG drop in some cases.

I would make these basic checks before assuming a critical part that the sophisticated ECM says is fine, is indeed not.

Barnabas

Hello,
Thanks for your input.
I already checked many things including what you pointed out, this would be my last attempt to fix the bad mpg, if this doesn't fix my problem I am selling this car which I love very much but I've put too much work into it
The part only says Upstream Front. and I can't find any more info into it..

Oro

Look above the cat on each bank. The sensor is threaded into the header pipe. Both are difficult to access, the back (bank 1) more so. The downstream ones are past the cat and much more accessible. If that doesnt help, google “1mz -fe oxygen sensor location” and you will see multiple images.

Your symptoms are really unusual and I hope you sort them out.

HomerJay

Some additional follow up questions, Is low gas mileage something that recently developed and how are you calculating MPG? Does the engine reach proper operating temperature?
Driving habits also have a big impact on MPG, what is highway MPG?

Barnabas

Low Mileage has been since I bought the car, highway I get between 19 and 21 and local I get between 11 and 14.
I get about 180-210 Miles per full tank I calculate it using the Trip A.

Thanks a lot