PFB

Background.

The car is a 2001 ES300 with approximately 82,000Miles. The Engine starts and runs flawlessly, yet I have experienced a sudden drop in average MPG from approximately 22MPG to 16 MPG. This over the last several months.

So my questions are the following:

1) Can a bad Oxygen Sensor cause such a drastic reduction in MPG yet, not throw any Check Engine light Codes, nor store any codes in memory (I have a Code reader)?

2) Would a bad O2 Sensor cause more problems in city driving than in Highway driving. I am asking that because my average highway MPG seems to have stayed the same, its my city average MPG that have take a major hit.

3) Assuming that it could be an O2 sensor, than could a well equipped Independent garage put a scanner on and pinpoint which O2 sensor it is?

Thanks,

Phil

frohboy33

You say you have a scanner. Can this read data in real time? If so please post your STFT(short term fuel trim) and LTFT(long term fuel trim) numbers. This can give a good indication of wether or not there is a problem.

1. A bad O2 sensor can cause bad gas mileage, but I haven't seen it where it doesn't throw a code.

2. I do think you would notice it more in city driving compared to highway.

3. They should be able to pinpoint which sensor it is.

PFB

Unfortunately, I Don't have a scanner, what I have is a code reader. My code reader will give me fuel trim info (Freeze Frame Data) but only when/if an engine code is present, otherwise it just indicates that all is normal.

Phil

frohboy33

Might want to pick one up from ebay. I got one for my 01 es300 for $15 it has helped me diagnose similar fuel problems.

exxonham

Hey bro I would say it could be the way you drive, I deliver pizza in mine and drive it pretty hard and get about 17-18mpg but I take good care of it. But it could be the way you gauge your mpg cause sometimes mine varies. But if it was an o2 sensor it should throw a code but you could always test all four of your o2 sensors, there is a diagram of the correct way to test your o2 sensor in ohms its floating around CL some where ill see if I can find it, just un plug the o2 wire with out takeing out the o2 sensor and a measure the ohms with a meter reder or tester the ohms should be bt two number not sure what that is but a meter reader is cheap under 10$ so I would try that before speanding money takeing it to shop or a shop should be able to Ohms your o2 sensors if you cant figure it out. Hope this helps

PFB

I was going to test the O2 sensors myself using an OHM Meter, but than I read that I have to remove the front Driver's side seat to get to some of the O2 sensor plugs. This is something I did not want to tackle.

So my next option is either to buy a cheap scanner off E-bay as suggested, or alternatively to bring it to a garage and have them perform a scan.

Thanks

Phil