why do i Have two O2 sensors before the Catlytic converter?

[darsh4126]

HI

I have daewoo lanos 1999 1.6L. I was surprised to find out that i have two O2 sensors before the catalytic converter(bank 1 sensor 1 and bank 1 sensor 2). What make sense is to have one O2 sensor before the cat and one after the cat(to measure the cat's efficiency), but in my case i have two O2's before the cat and none after the cat.

I understand how one O2 sensor would switch between lean and rich so the ECM would provide fuel in a effective manner, but what does that second O2 before the cat is doing over there.

Can somebody explain this to me.

Thanks
Darsh

[MMamdouh]

i think you have two cats... one right after the exhaust mani and the other is underneath the car... your O2 sensors are located at the bottom of the exhaust mani (before first cat) and the second is in the area under the engine (after the first cat and before the second cat)

MMamdouh

[darsh4126]

Maybe you are right, but according to the service manual i only see one cat.

thanks
darsh

[Daniel]

Intersting. Where are you located? Can you post a pic of those two sensors?

[darsh4126]

I have one O2 sensor on the top of the exhaust manifold(under the hood), the second one is underneath right before the flex pipe(cat is in the middle and it is before the cat). I'll post a picture when i get a chance. I am here in US, California.

Darsh

[benzino]

because, california...

[darsh4126]

What i am trying to figure out is that what is that second O2 sensor before the cat is doing. In usual case you have one O2 before cat and one after the cat.

[Daniel]

IMHO,
First O² sensor try to control air/fuel mixture feeding engine.
The second O² sensor is there to control if first cat (pre-cat) is doing its job correctly.

[darsh4126]

thanks again for the reply. You see i agree with you if I have two cats, but i only have one cat( i inspected it visually, and i don't see anything in the service manual either).
My check engine light was flashing couple of times when i was in the free way, and as soon as i turned off the engine and restart it went away. I have ElmScan 5, and i recoded the whole trip while the check engine light was flashing, and still no code. This does not happen all the time.

When i ran the recoded data i saw that my fuel system status was going into open loop 11 times(each time it was about 6 second, some 8 seconds, two time it was 11 seconds). So, looked at the O2 sensor values, and they show 0 volts some times, and below 0.1 sometimes. So i went ahead and replaced both O2 sensors.

Then i recorded a another trip, but MIL did not flash. However, when i ran the recoded data i still see it is still going into the open loop with low O2 sensor values. My coolant temperature is about 179F-185F. I am just thinking maybe my engine is not warm enough.

[gse_turbo]

I know I'm coming late to the game but I just want to confirm. there is not cat hanging from your exhaust manifold OR there is no cat in the exhaust right at the drivers feet?

every Daewoo since OBD11 has had two cats, if you don't have both those cats then someone has removed it and there would most likely be a problem.

as for the open loop. is this happening randomly? the ECU will go into open loop when the throttle is above 80% open (give or take).

[darsh4126]

It went to open loop with even 4.7% throttle. I do not notice any change in performance. My check engine light was flashing, and it was very random. My service manual does not even say that i have two cats. You may be right there can be a cat that is hanging from the intake manifold.

[benzino]

the service manuals that you get are older than the OBD2 models (or non-NAM models) so they will only show 1 cat

[Daniel]

Here's what I found on the website Bosal. It seems to be two catalysts 099-1009 & 099-243.

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[darsh4126]

Okay thanks Daniel and Benzino for finding this information, now this all make sense. Also guys i need help with my engine misfire situation. I already post a new thread call engine misfire.

Can you guys help.

Thanks

[benzino]

does yours look like that?
a small cat at the manifold and a larger one in the normal spot?