blizza

My o2 sensor was left out by a mechanic and I drove with it like that for a week until the check engine light came on telling me my o2 sensor was bad. I put a new o2 sensor in and then two weeks later the check engine light came on again with a different code, code p0420, catalyst below threshold Bank 1.

Does this mean my cat is bad (because the o2 sensor was left out I'm guessing) or could it mean something else like the back o2 sensor? How can I be sure before buying a new cat?

ezone

Why isn't the mechanic going to fix his mistake, along with any damage it caused?


Why was it left out?
If it was missing, didn't you notice a lot of unusual noise?

blizza

Guess I should mention that it's a 2003 civic ex automatic.

The shop is now denying that they left the o2 out, even though they initially acknowledged it and put a new one in for free (that I bought). But now that I'm getting the catalytic code, they refuse to replace it and say they didn't cause it.

As for while o2 sensor was out (it actually wasn't all the way out, just so loose that I removed it with one turn of my hand), I didn't notice anything major being wrong until the check engine light came on. I thought I noticed some poor gas mileage but nothing more than that.

So, now I'm getting the catalytic p0420 error, but I've been driving the car with no problems that I can tell. I'm still getting 350-400 miles per tank consistently. Maybe it's a little slow accelerating, but I can't really tell for sure. One other thing I notice is that when idle with the a/c on, the car sometimes vibrates pretty badly, but I think that might just be a bad motor mount or something.

Do you think the p0420 code means the cat is shot?

ezone

What work was performed by this shop, what was done to the car that necessitated touching the O2 sensor in the first place?

So now it wasn't actually missing?

None of us can say if a cat fail code was caused by anyone.
We need to know more about the conditions before it failed.
Has it run very poorly recently? Ever?
Did it have a cat code before?
Did it have a CEL on before this, without you knowing the codes?
Has this cat code been erased and the car driven, to see how long it takes for the code to return?
How many miles on the car?
Does the engine consume oil?

What exactly did you buy? (brand and part number)

The computer judges both Oxygen sensor readings to determine if the cat is doing its job correctly or not. If either sensor is not reporting accurately, that could cause the cat self test to falsely fail. Non-original brand sensors have been known to cause problems.


If the computer has accurate control of fuel delivery, if there are no exhaust leaks, and a few other checks, then the cat failure code can be judged as true and the cat is replaced.