Question about o2 sensor

Hi everyone,

I have my Tacoma, 2002, 4 door, v6, auto transmission. The gas miles only 15. We know that there are 2 sensor, the one before or the one after the CAT affect gas miles ?. So if that, then which one i should change it?
Thank for your help
THONGO

 

Do you have any cel codes on dash?

 

before cat is the one that has an effect on mpg the 2nd o2 monitors the cats function. rockauto.com has great prices on the denso 02s you can have slow switching o2s with no codes

 

I have no check engine light on yet. But I think cause of bad o2
Thanks

 

Have you done a good tune-up? That mileage not too good. Don't think a 02 is gonna get you where you should be.

 

Yes, the truck run really good, change oil every 3k, spark plug,fuel fifter all change. I think my o2 not working good. It make my truck 15 mpg
Thanks

 

Air filter, pcv valve, clean maf, clean throttle body, wires could also help. I'm sure there are more little things that would help. The 02 sensor is about 100 bucks. Might try little things first.

 

I read a thread recently that stated O2 sensors should be changed every 80k miles. For one they can cause your catalytic converter to fail which is an expensive fix. Also, if they are bad then they may cause bad gas mileage.

I just replaced my stock sensors and cats after 175k miles and they have been bad for the past year or so at least. I had the entire emissions system diagnosed twice and they both stated that the O2 sensors caused my catalytic converters to fail, more importantly the first cat and 02 sensor (A/F sensor).

Take this info/ experience with a grain of salt because I'm sure there are many people who have heard or experienced otherwise.

 

FWIW, I just changed both sensors at 135K miles. Had a CEL P1135 which is the heater portion of the upstream (before the first CAT) sensor.

I was surprised at the change in the way the truck drives, at least initially. It may be because I had the battery disconnected so the ECU is starting over clean and may be adapting and getting back to the way it was before the change.

What I noticed first after the swap was a slight reduction in low end torque. Also, a slight drop off in power at the top end of the gear (right before it shifts). Before I made the swap and even with the CEL on, the truck was running like a scalded cat.

What is interesting is that either I am getting used to the difference and it is becoming the norm, or the ECU is adapting to how I drive. The torque loss seems less now and it is reving easier/better.

And on the first tank after the change, MPGs are up. Maybe 2 mpgs. That is scangauge data and not a complete tank and refill calculation.

 

https://www.google.com/#q=234-9001+$100..$200&tbm=shop&tbs=vw:l,p_ord:p

Ed

 

https://www.google.com/#q=234-4189+$10..$100&tbm=shop&tbs=p_ord:p

Ed