Strange downstream O2 sensor behavior?

[perseuss69]

Hi

About a week ago I got a P0430 - Catalyst System Efficiency Below Threshold (Bank 2) code, that I cleared and hasn't come back. From what I understand that could be caused by: bad O2 sensor/s, cat failure, exhaust leak, and perhaps even from short trips during cold weather.

Now, today, after some driving I had the car idling at operating temp and decided to take a look at the OBD2 readings, since it was idling a bit too high. I saw that one O2 was at 0,8V and the other at 0,1V. That seems odd. I've added a short video of the car idling and applying light throttle for a second.

Any thoughts on what could cause this? Exhaust leak? Bad sensor/s? Also as a side note: the car is and has been for a long time, running quite rich. LTFT1 at -20% and LTFT2 at -10%.

Thanks.

[ColinBarber]

4 hours ago, perseuss69 said:

Any thoughts on what could cause this? Exhaust leak? Bad sensor/s?

Looks like an exhaust leak at or before the downstream O2 sensor in bank 2 which is keeping the sensor reading lean (0.1 v) at idle.

[perseuss69]

15 hours ago, ColinBarber said:

Looks like an exhaust leak at or before the downstream O2 sensor in bank 2 which is keeping the sensor reading lean (0.1 v) at idle.

Thanks! I'll be taking the car to a shop tomorrow and see if they spot anything.

[perseuss69]

On 1/10/2024 at 12:22 AM, ColinBarber said:

Looks like an exhaust leak at or before the downstream O2 sensor in bank 2 which is keeping the sensor reading lean (0.1 v) at idle.

There were quite a few leaks on both sides, interestingly. European salty winters make quick work of Japanese cars it seems. But they should be fixed for now and both O2 sensors read 0,9V at idle. I was hoping it would have some effect on the long term fuel trims as well, but no luck. I guess it's just due to weak compression or a mix of things.

[ColinBarber]

1 hour ago, perseuss69 said:

I was hoping it would have some effect on the long term fuel trims as well, but no luck. I guess it's just due to weak compression or a mix of things

Not unless there are holes up at the manifold as it is only the upstream sensors that affect fuelling. Probably a combination of lazy upstream sensor, carbon build up, injectors leaking/not atomising the fuel etc.