O2 Sensors with High Mileage

[2002 Maxima SE]

This a new one on me. My 2000 Ford Taurus recently had a drop in mileage to 17 mpg. At first, I thought it was a bad tank of gas but a second tank confirmed it. No codes, regular oil changes (of course) and top tier fuel. The fuel pump and regulator have been replaced last year due to failure.

After some research, I decided it could be the OEM O2 sensors. I used my BlueDriver scanner to pull fuel trims and voltage. Nothing seemed out of the ordinary (to my untrained eye). The O2 sensors by NTK are cheap enough ($25 each) so I replaced them a few weeks back.

I was about 1/4 into the new tank of fuel, so I was not expecting major increases in fuel economy. I filled up last night and got 22.6 mpg. My best fuel economy is 24 mpg on highway and 20 mpg around town.

All in all, I am very pleased with the results! Side-by-side comparison of the short-term fuel shows slight variations between old (blue/red) vs new (yellow/green) which I suppose is enough to lower the fuel mileage.

 

[zrxkawboy]

I usually replace upstream O2 sensors at around 100k miles as preventive maintenance. They can get "lazy" which lowers MPG without throwing a code.

 

[Marcozi]

O2 sensors get lazy as they age. That is, they don't respond to changes in the exhaust stream as quickly as new/newer sensors. They are considered maintenance items.

 

[SHOZ]

On my Accent I changed out the OE primary sensor at around 100k with a aftermarket Bosch, kept the old one though. The replacement failed at about 150k miles. But I drove it into the ground. I was watching the O2 sensor voltage both pre and post cat while this was going on.

Really no change in fuel mileage until it did fail and stopped reacting. The ECU then set a code and was using the static fuel tables. Car ran alright but was running much richer than with the O2. Ended up putting the original back in for another 30k miles or so then got another OE.

 

[edyvw]

100k and they are out, CEL or not. They become "lazy."