Hi all! I have a 2004 Hyundai Elantra that is having problems getting the Cat test to go complete. It is stuck as incomplete and has a pending P0420 code. The code has been pending for the past two weeks, maybe longer as that’s when I first started checking because I wanted to get inspected. This is…

Here’s what the O2 sensor signals should look like. [image] Tester

So what you’re saying is it could be both (Upstream O2 and cat going) or are you leaning towards just the cat starting to go?

Both lines on your graph are labeled downstream. The computer enters the closed loop mode when coolant reaches operating temperature. It doesn’t matter if the sensors are working or not. Tester

Oh okay, that explains the fuel system loop question. I thought that O2S1 was upstream and O2S2 were downstream, since they’re both bank 1 if I’m reading it right.

You would have had some driveability issues like lacking power and bugging down if it was the cat.

So you’re leaning towards it being the O2 Sensor if I’m correct? Do you think it’s the O2S1 sensor like I was alluding to above? I don’t have any driveability issues, just the CAT monitor staying at incomplete with the code staying at pending, it won’t go away or set permanently. If I erase it it ju…

If the green line is the downstream O2 sensor, the cat is bad. Tester

[image] ryan77627: I thought that O2S1 was upstream and O2S2 were downstream, Correct O2s1 is upstream O2s2 is downstream you’ve got way too much activity on the downstream sensor . . . that’s why you’re getting P0420 as a pending code Conversely, there’s not much going on, as far as the …

Don’t look like you had a hot enough engine when the graph was captured. Sensors don’t work or work correctly until the exhaust is at around 640 degrees. According to this, I would change the downstream sensor. $30 if you do it yourself.

More ideas . . . With everything warmed up . . . after those several miles of spirited driving I mentioned . . . create an extremely large vacuum leak at idle How does the upstream sensor react? It should very rapidly show a very low reading, such as 50 or 100 millivolts If it can’t do that, the…

Bad O2 Sensor or Cat Problem?

Maintenance/Repairs

Tester July 26, 2020, 5:35pm 2

Here’s what the O2 sensor signals should look like.

Tester

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Bad O2 Sensor or Cat Problem?

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