Am getting low MPG, avg. of max. 19 MPG on higways, so i started diagnosing O2 sensors with a scanner.

Can some one tell me why my car' s downstream-post-cat O2 sensors on both banks 1 & 2 are too low its showing only 0.04 volts while engine idling. I have read in some sites that post cat O2 sensors output should fairly steady average 0.45 volts or higher.

Upstream-pre-cat O2 sensors readings on idle are fine, crosscounts between 0.2 and 0.8 Volts on both banks.

Also noticed that short term fuel trim reading on idle are 5% on both banks, but long short term fuel trim reading are high showing 20% on both banks.


Can someone help!
Any one who get 22+MPG ? Can you post your O2 sensors readings on idle!

 

Actually believe it or not, I have the same issue with my car with the mpg not going more than 18 to 19 on the average and I did a massive tuneup in the engine, including all seals, plugs, fluid flush, timing belt, accessory belt and coolant temp sensor but it just doesnt seem to improve at all and I do most highway driving and it used to give me at least 22 in the city and 28 on the highway but it barely shows me 22 on the highway but it never does. And we both are in UAE, is it something to do with the fuel here as cars run great initially and then mpg suffers over time, at least that is what happened to me.

Ok if you do not mind me asking how to check the readings and the location of the sensors and I will do the procedure and report back here. I will be glad if it increases as I really love the car and dont know why the mpg dropped and I do not drive with a lead foot and accelerate slowly and rpms rarely go more than 3.

 

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coolant temp sensor

i have not tried to replace mine yet, did u replaced it with OEM part?

No its not, one of my friends, have 98 LS400 and he gets 26MPG on most highway driving. Unfortunately I couldn’t have a chance to scan and read his car’s O2 sensors volts outputs on idle to compare it with mine.

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Ok if you do not mind me asking how to check the readings

You need OBD2 scanner or OBD2 interface.

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location of the sensors

There are total of 4 oxygen sensors.
one comes before cat on both banks 1 & 2.
one comes after cat on both banks 1 & 2.

Bank 1 is the driver side.
Bank 2 is passenger side.

More info. About O2 sensors read here
http://www.aa1car.com/library/o2sensor.htm

I don’t want to replace parts without diagnosing them first.

Guys any one who gets 24MPG or more on highway driving, could you please post your car’ s O2 sensors reading on idle. This will help me to compare the readings with my car.

 

[QUOTE=qewani1;6250672]
i have not tried to replace mine yet, did u replaced it with OEM part?


Yup replaced with OEM part.