oxygen sensor for '02 Celica GT

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Eosyn

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Jul 15, 2011
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Hiya folks.
Ever since I had my upstream and downstream o2 sensors replaced about 2yrs ago, my gas mileage went down (37 mpg to 30 mpg roughly) and, the worse thing is, she doesn't shift into 4th gear (she's an automatic) until the engine is warmed.

I read it is due to faulty O2 sensors and I plan on replacing them this summer. The question is, are the harness for the up/down stream labelled so I'll know which to hook it up to. Reason I ask is that I'm not sure if the guy who changed it originally plugged them into the right ones or not.

Thanks in advance!
 
Thank you for bringing this up. I have a bad upstream oxygen sensor too in my 04 Civic.
I have check engine light on for about 3-4 months. I asked dealer but they gave me really high price to fix it so still driving like that.

The car runs well but recently last few days, when I start rpm is around 1500 which pretty high. It was not that high before. (outside temp is pretty much same FL
smile.gif


Is it related to O2 sensor? Does it harm anything if I keep driving without changing the sensor?
 
Originally Posted By: CivicLX
Thank you for bringing this up. I have a bad upstream oxygen sensor too in my 04 Civic.
I have check engine light on for about 3-4 months. I asked dealer but they gave me really high price to fix it so still driving like that.

The car runs well but recently last few days, when I start rpm is around 1500 which pretty high. It was not that high before. (outside temp is pretty much same FL
smile.gif


Is it related to O2 sensor? Does it harm anything if I keep driving without changing the sensor?

The front sensor is the important one, but is your can an automatic? Does it still lock the torque converter in top gear?
If it still locks up then its probably only the O2 sensor heater element that's gone and replacement is sort of optional. I drove my Tracker for a few years until I could buy a sensor for a reasonable price. If you want to avoid a possible headache, just go to a good independent garage and get them to change it, I'm guessing it will be $100-150 total.
 
Woot!! Thank you much...I'm gonna change them both sometime this weekend.

BTW, is there a difference in Premium oxygen sensor vs. one that isn't "premium?"
 
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Originally Posted By: CivicLX
Thank you for bringing this up. I have a bad upstream oxygen sensor too in my 04 Civic.
I have check engine light on for about 3-4 months. I asked dealer but they gave me really high price to fix it so still driving like that.


Is it related to O2 sensor? Does it harm anything if I keep driving without changing the sensor?

You're welcome
grin.gif


From what I understand, running with bad 02 sensors will decrease your power and drink up a lot of gas (immediate affect). Over-time they say it will destroy your catalytic converter (which I hear is expensive to replace).
 
Originally Posted By: Eosyn
Woot!! Thank you much...I'm gonna change them both sometime this weekend.

BTW, is there a difference in Premium oxygen sensor vs. one that isn't "premium?"

Definetely get a good brand name one, a quick search on a forum for your car should help you figure out if one brand is prefered or to be avoided.
 
i would not put anything but an OE 02S in that car. Expensive, but it will perform the way it is supposed to.
 
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Originally Posted By: mattd
i would not put anything but an OE 02S in that car. Expensive, but it will perform the way it is supposed to.


Oh definately. I wouldn't want to even try a universal fit and mess with all the wiring. Straight OE for me
thumbsup2.gif
 
Amazon has both Denso 02 sensors for your car at a total price of $120ish.
$58.75- 234-4623
$61.12- 234-4604

You've probably already seen it, but just in case.
Hope you get things back to normal mpg wise...
 
Oh very cool thanks! I already installed a Bosch yesterday and last night (cool night out) driving to work, it didn't fix the shifting, so will replace the downstream one sometime soon and see if that will fix it.

Thanks for the links!
 
very good question. You're the first one to bring up the thermostat. I'll have to look into that.

I made an error on the mileage, looking back at my hand written log, I was getting 35 mpg, then it dropped to about 30, on average.

Thanks for the suggestion
smile.gif
 
Originally Posted By: Virtuoso
A failing o2 sensor not allowing converter lockup? Is this typical for some makes?


1. I read on youtube that this person had the same problem and he said it turned out to be a faulty O2 sensor. It will not shift to the next gear until the engine is warm. so it will go up to 4k rpm until the engine is warm, then it shifts to the next gear.

2. No idea if this issue is typical for my '02 Celica or not.
 
Originally Posted By: Virtuoso
A failing o2 sensor not allowing converter lockup? Is this typical for some makes?

If the front O2 sensor, which monitors the fuel ratio, doesn't work, then the ECU can't go into closed loop mode. On some cars this will prevent the ECU from locking the TC.
 
Update:
laugh.gif
I replaced the upstream oxygen sensor (Denso) with a Bosch sensor (cost me an arm at the local autozone). It seems to improved my gas mileage a bit, but still in the process of getting data. It also seems to help a bit with the shifting into 4th gear, it doesn't take as long to get warm, then it shifts just fine.

Next question is: what does the downstream O2 sensor do and should I replace it also? I'm hoping if I do replace it, it will help with the gas consumption and completely get rid of the shifting problem, but I'm skeptical. Your thoughts?
 
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Update: The fuel mileage I'm getting with the new upstream O2 sensor is 33 mpg (up from 30 at best with the old one). Though that is only the first tank after the replacement, I will see if this number can be replicated with future fill-ups.
 
Originally Posted By: asand1
FWIW I bought my o2 sensor from rockauto. It was a Denso direct fit and cost $50 shipped. Local was $120.


I should have looked at rockauto before I bought mine for $110 @ local autozone. Well, lesson learned, will buy from rockauto for my family sedan, the '05 corolla.
 
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