Thread: How many O2 sensors??

I recently had the check engine light come on.
I first took it to AutoZone, then took it to the dealer & was told an O2 sensor was bad (same thing as what AutoZone's computer said). I don't know which one it was...all I know is that he removed it from the area between the rear of the engine & the firewall.
He reset the light & I traveled happily for about 75 miles when the light came on again. I didn't take it to the dealer (could afford another $175 for diagnostics & parts replacement), but to AutoZone. Their computer again stated an O2 sensor, this time a different "bank".
Just how many O2 sensors does this thing have?
My fuel mileage is taking a beating!
Thanks!

Originally Posted by Toofastgs

There is 2 sensors.

""ll I know is that he removed it from the area between the rear of the engine & the firewall""

So they physical removed this sensor? if so need to get it replaced. Your car should not be running right.

Yeah, he removed & replaced it. I hope my waiting to replace the other(s) won't cause the new one to wear out prematurely.
I was told that there was one in the front of the engine & one underneath.
Where's the 2nd one at?
Thanks!

Originally Posted by Sabrewings

There is one in the rear manifold (the one that they replaced) and there's one under the car in the down pipe.

So when I go to the parts store to get one (they show 2 different ones), which do I get?

Sorry, but I don't remember the exact code.
All I can remember was that the mechanic said that the code that came up showed the manifold sensor (can't remember which bank) & after that was replaced, the other bank showed up on the code.
When he had his computer hooked up to it, he showed me on it that the sensor wasn't working as it should...acting kinda "lazy" & then showed me afterwards how the new one was performing as it should.
He also mentioned it could possibly be a fuel injector issue, but unlikely since I told him it was running fine.
I can get the code for you if you'd like later today.
I've got it scheduled to get worked on Tuesday. I get free labor where I work at...just gotta supply the parts.

ive heard that the bosch o2 sensors are garbage. Dont know for sure but you might want to look into it

What year is your car?

The rear 02 doesn't really do anything for performance or your engine, it basically is there to make sure you have a cat or that its working halfway decent in basic terms. Most people just buy an 02 simulator instead. 02 simulators run about $45 new, you just plug it in and tie the wire up in the engine so it doesn't get burnt by the exhaust manifolds. Then either clip the wire off the bad 02 and leave it in, or pull it out and put a plug in.

02 simulator is probably a lot cheaper than a new 02 sensor, and you dont have to worry about it again.

Now on 01+ cars (correct me if im wrong on the years), the pcm goes through a diagnostic check when it senses the rear 02 is bad, causing the engine to run rich and sometimes at idle it will float the rpms up and down. As long as the pcm is getting a signal from the rear 02, it will not do this diagnostic cycle, so the simulator is always needed, even if you have a tuner to delete the codes, it will not go away unless there is a sim.

Originally Posted by FoSHO99

What year is your car?

The rear 02 doesn't really do anything for performance or your engine, it basically is there to make sure you have a cat or that its working halfway decent in basic terms. Most people just buy an 02 simulator instead. 02 simulators run about $45 new, you just plug it in and tie the wire up in the engine so it doesn't get burnt by the exhaust manifolds. Then either clip the wire off the bad 02 and leave it in, or pull it out and put a plug in.

02 simulator is probably a lot cheaper than a new 02 sensor, and you dont have to worry about it again.

Now on 01+ cars (correct me if im wrong on the years), the pcm goes through a diagnostic check when it senses the rear 02 is bad, causing the engine to run rich and sometimes at idle it will float the rpms up and down. As long as the pcm is getting a signal from the rear 02, it will not do this diagnostic cycle, so the simulator is always needed, even if you have a tuner to delete the codes, it will not go away unless there is a sim.

It's an '02.
The local parts store (NAPA) has the 02 sensors for about $60. Probably easier to mess with than rigging it, yes?

Originally Posted by Tullphan

It's an '02.
The local parts store (NAPA) has the 02 sensors for about $60. Probably easier to mess with than rigging it, yes?

Not necessarily, I would buy an simulator before I would buy another aftermarket 02. You could easily install it.

Here it is:
ZZ Performance

Just out of curiosity, if the O2 sensor on the exhaust don't really do anything, why is my gas mileage still down 5-6 MPG? Would a bad O2 sensor on the "downstream" affect fuel mileage?
Someone earlier stated that Bosch O2 sensors were junk. Are they bad from the start?

Originally Posted by Tullphan

Just out of curiosity, if the O2 sensor on the exhaust don't really do anything, why is my gas mileage still down 5-6 MPG? Would a bad O2 sensor on the "downstream" affect fuel mileage?
Someone earlier stated that Bosch O2 sensors were junk. Are they bad from the start?

Like I said, years 01+ have some diagnostic cycle they go through when it detects a defective 02 sensor. This diagnostic cycle causes the car to run rich, killing gas mileage and no one has access to this in the pcm to turn it off. I have a powrtuner, if mine was a 98 or something I could just delete the codes for the 02 sensor when I take it out but I can't with my 01, it goes through this cycle still with the codes deleted.

Just get a 02 simulator. Also, if you look under your car and see that big hump where the rear 02 is right now, you will notice its constrictive. Taking that 02 out and replacing that pipe with a straight one could increase your hp and gas mileage... Its actually one of the first mods everyone does.

Originally Posted by FoSHO99

Taking that 02 out and replacing that pipe with a straight one could increase your hp and gas mileage... Its actually one of the first mods everyone does.

If I did that, would the computer recognize it was missing? Or are you talking about getting a simulator AND doing that?
I guess i'd need to have a friend that owned a muffler shop to do that, yes?

the 02 simulator replaces your 02 sensor. All the 02 simulator does is provide a fake signal so your pcm detects that its there and working. Since the pcm knows its there and working, it will not throw up a DTC.

A shop will have to weld in the pipe if you want. You could buy this and then have them weld it in or just have them put in a pipe of their own.
ZZ Performance

OK, so let me get this straight.
If I go the emulator route, I leave the old O2 sensor where it's at & unhook it? Then I use the wiring harness that went to the old O2 sensor, hook it to the emulator, bundle it up & secure it in the engine compartment somewhere?

Originally Posted by Tullphan

OK, so let me get this straight.
If I go the emulator route, I leave the old O2 sensor where it's at & unhook it? Then I use the wiring harness that went to the old O2 sensor, hook it to the emulator, bundle it up & secure it in the engine compartment somewhere?

Yes. You could also take the 02 sensor out and put in a plug instead, either way.

I took the car to autozone again to see why the check engine light's still on.
They didn't give a specific code, but said "bank one is running rich".
I asked about the chances of a new O2 sensor going bad & he pretty much said "slim to none".
Where can one find an AC/Delco O2 sensor reasonably priced?
I don't think it's an injector issue since it runs good. It's just getting less (3-4 mpg less) gas mileage than before.
Thanks.