Front O2 Sensor Cooked After 70k Miles?

[Robb235]

When I bought my rig 2 years ago it had 190k miles on it, and one of the first things I did was replace the front O2 sensor because it was getting terrible mileage. That fixed my fuel consumption problem. Now, lately, it's been getting terrible mileage and down on power. Last night I was wanting to get home, so I drove 80mph on the interstate, but was having to really flog the motor in order to maintain that speed. I know it's winter time, and winter blend fuels cause mileage to go down, but my fuel mileage is much worse than usual.

I cleaned the MAF, tire pressure is good, and air filter is new. I've got 263k miles on the truck now. I've got California emissions, so it's actually an air/fuel ratio sensor (aka wideband O2) upstream. Could it have already worn out after 70k miles?

 

[thebrandon]

What brand sensor is it?

 

[Robb235]

Denso.

 

[rangermenace]

What does flog the motor mean? :shrug: what do you think is bad gas mileage, mine is getting like 15 mpg around town. Wouldn't a bad sensor set off an engin light?.

 

[Arnezie]

No codes then your most likely looking at the wrong thing

 

[MONTYMTB]

No codes then your most likely looking at the wrong thing

Not necessarily, according to this article.

 

[JayRolla]

Denso.

Toyota OEM or parts store denso?

 

[gamefreakgc]

DENSO O2 Sensors for these trucks have a life of roughly ~90k miles. I couldn't find specifics for 3rd Gen, but 2nd Gen (almost identical part) are clearly stated to only last about 90k miles.

Over time carbon deposits, foreign materials and other normal exhaust gases will build up on the O2 sensor causing it to react slower and eventually read O2 levels incorrectly. These sensors don't usually fail catastrophically (unless the heater circuit shorts), they will fail slowly over a long period of time.

OP, remove your O2 Sensor and take a look at it. If it's covered in soot and looks clogged then it's time to change it.

P.S. O2 sensors are a little like spark plugs. If they are a white/ash color, then your engine is running correctly. If they are black you're running rich, and if slick/oily then you are burning oil. It's not an exact science but can give you a clue on what is going on if it really is failing early.

 

[Robb235]

Toyota OEM or parts store denso?

Bought it on Amazon, so probably not OEM.

 

[Robb235]

DENSO O2 Sensors for these trucks have a life of roughly ~90k miles. I couldn't find specifics for 3rd Gen, but 2nd Gen (almost identical part) are clearly stated to only last about 90k miles.

Over time carbon deposits, foreign materials and other normal exhaust gases will build up on the O2 sensor causing it to react slower and eventually read O2 levels incorrectly. These sensors don't usually fail catastrophically (unless the heater circuit shorts), they will fail slowly over a long period of time.

OP, remove your O2 Sensor and take a look at it. If it's covered in soot and looks clogged then it's time to change it.

P.S. O2 sensors are a little like spark plugs. If they are a white/ash color, then your engine is running correctly. If they are black you're running rich, and if slick/oily then you are burning oil. It's not an exact science but can give you a clue on what is going on if it really is failing early.

Thanks for the info. I wasn't sure what the expectancy was on these things. I guess I'm starting to get close to the end on mine.

 

[animator]

Got roughly 65k on my first rear sensor, with the heater circuit failing on it. Around 110k on the first front. I'm at 176k now with both still working. Probably time for one of them to fail again, but unless the heater fails, I'll never know. O2 Simulator is keeping my MPG at 18 and my check engine light in the off position.

 

[19963.4lsr5]

Generally if the sensor is going bad it will code. And since yours is the wide band sensor......more so. IMO of coarse.

Have you considered that your CAT could be clogged?

Funny though when I bought the 1996 there was every indication that both O2 sensors were the original sensors. The nuts were all but rusted off when I replaced the exhaust from the CAT back.

 

[Robb235]

Generally if the sensor is going bad it will code. And since yours is the wide band sensor......more so. IMO of coarse.

Have you considered that your CAT could be clogged?

It's possible. I unbolted it from the exhaust several months ago (for an unrelated project), and while I had it off I looked at it and it didn't appear to be clogged. I guess that could have changed between then and now.