P2096 is being persistent. (Downstream O2 sensor)

[Fummins]

More derailing here. I replaced the ntk or ngk o2 sensor I installed the other day with an oem one from gm. Then I realised I should do a fuel trim and o2 sensor reset thing. So I did those and now all seems good in the hood.
For now.
It'll be back tomorrow morning with the same issues guaranteed.

Any*****...The most common cat code I see in the Mirage is usually a p0420 and sometimes a p0421. I usually just keep clearing them until I finally just replace the cat and with a used one that i have laying around. They usually crap out around 300,000km/186,000miles like clockwork. I've been lucky and just reused the old "gaskets". I had one higher mileage car throw a lean code for a while and it was hard to start after fueling up. The purge valve or solenoid on the side of the cylinder head was the problem with that one.

[AtomicPunk]

Any*****...The most common cat code I see in the Mirage is usually a p0420 and sometimes a p0421. I usually just keep clearing them until I finally just replace the cat and with a used one that i have laying around. They usually crap out around 300,000km/186,000miles like clockwork. I've been lucky and just reused the old "gaskets". I had one higher mileage car throw a lean code for a while and it was hard to start after fueling up. The purge valve or solenoid on the side of the cylinder head was the problem with that one.

That's really not too bad at 186k miles, given how cheap the rest of the cars materials are. Have you priced any new one's (cats)? Just curious. Side note: just bought my sister-in-law's 2003 Envoy for my soon to be 16 y/o son. 175k miles, paid $1000. Have spent $2600 so far fixing crap. But mom wants him in a tank, which it is. It's an xlt, 19 years old, and more tech/bells and whistles on it than my G4. And a cool 15mpg from the straight 6, lol.

[Fummins]

That's really not too bad at 186k miles, given how cheap the rest of the cars materials are. Have you priced any new one's (cats)? Just curious. Side note: just bought my sister-in-law's 2003 Envoy for my soon to be 16 y/o son. 175k miles, paid $1000. Have spent $2600 so far fixing crap. But mom wants him in a tank, which it is. It's an xlt, 19 years old, and more tech/bells and whistles on it than my G4. And a cool 15mpg from the straight 6, lol.

I had an 03 or 04 envoy for one winter. It wasn't too horrible on fuel if I didn't floor it everywhere. I remember it being a bit of a dog down low but it would just keep on revving if you held it to the floor lol.

[Cani Lupine]

The spark plugs and coils were replaced some time ago, long before I had this code pop up. However, I didn't reset the ECU by pulling the battery this time. I only cleared out the trouble codes.

It does seem that both O2 sensors are giving the same readings for a rich mixture.

As for why it would give a lean code, I would need to understand the logic behind the code, whether it's actually reading lean or if it has to compensate for excess air beyond a certain amount. Unfortunately, I don't know if there's a way to find out.

The car has 115k miles on it now, so some things are starting to get old on it. Both O2 sensors were replaced within the last 10k miles.

[Fummins]

Did you use dialectic grease on the connectors by chance? I read that’s a no no for some sensors cause they somehow vent thorough the wires themselves.

[allrock]

The spark plugs and coils were replaced some time ago, long before I had this code pop up. However, I didn't reset the ECU by pulling the battery this time. I only cleared out the trouble codes.

It does seem that both O2 sensors are giving the same readings for a rich mixture.

As for why it would give a lean code, I would need to understand the logic behind the code, whether it's actually reading lean or if it has to compensate for excess air beyond a certain amount. Unfortunately, I don't know if there's a way to find out.

The car has 115k miles on it now, so some things are starting to get old on it. Both O2 sensors were replaced within the last 10k miles.

TECHNICAL DESCRIPTION
The signal from the heated oxygen sensor (rear) differs from the linear air-fuel ratio sensor, because the catalytic converter purifies exhaust gas. When the catalytic converter has deteriorated, the signal from the linear air-fuel ratio sensor becomes similar to the heated oxygen sensor (rear).
The ECM compares the output of the linear air-fuel ratio sensor and heated oxygen sensor (rear) signals.

deteriorated cat makes both front and rear readings nearly identical.

[klroger]

TECHNICAL DESCRIPTION
The signal from the heated oxygen sensor (rear) differs from the linear air-fuel ratio sensor, because the catalytic converter purifies exhaust gas. When the catalytic converter has deteriorated, the signal from the linear air-fuel ratio sensor becomes similar to the heated oxygen sensor (rear).
The ECM compares the output of the linear air-fuel ratio sensor and heated oxygen sensor (rear) signals.

deteriorated cat makes both front and rear readings nearly identical.

See post 34

[Cani Lupine]

I actually did not use dielectric grease.

On cat deterioration, that would make sense if I was getting P0420, but I'm getting a code for a lean condition that isn't there. That's the confusion.

However, it does seem like my cat is dead.

[klroger]

I actually did not use dielectric grease.

On cat deterioration, that would make sense if I was getting P0420, but I'm getting a code for a lean condition that isn't there. That's the confusion.

However, it does seem like my cat is dead.

Lean means there is too much O2 in the exhaust gas. As the converter works, it takes O2 out of the exhaust gas to use in the catalyst reaction. . The cat monitor is seeing too much O2 in the exhaust gas if the catalyst isn't working. I think you're confusing the Lean description of the cat monitor with a lean engine condition, which is not the same... The ECU does not use the Cat monitor to adjust fuel trims. It only monitors Cat performance. It's confusing because they call it an O2 monitor (which it is) but it's easy to get thinking it's the same as the upstream sensor. Hope this kinda helps explain it.

[Cani Lupine]

That would make sense, perhaps the ECU is misinterpreting the signals and giving the wrong code. The logic flowchart for "Post-catalyst fuel trim system too lean" I've seen doesn't quite seem to fit.

Though the thing that I can't understand about that is the downstream sensor reads consistently rich, so if it was getting excess oxygen, wouldn't the voltage be low?