Recently I've swapped my catalytic converter with another used one due to P0420. My Bank 1 Sensor 2 was mimicking the bank 1 sensor 1, so it was definitely a bad cat.

After I've swapped it, everything seemed to be fine  -- Bank 1 sensor 2 was always low and bank 1 sensor 1 going up and down as it should.

This happened 2 months ago.

 

Yesterday, the check engine light came up again and upon checking it was P0420.

I looked at the graphs and the bank 1 sensor 2 wasn't mimicking the bank 1 sensor 1. However the bank 1 sensor 2 was pretty stable at high values, then it dipped for a period, then back up.

My initial thoughts were that the Bank 1 Sensor 2 might be faulty itself.

What do you guys think?

 

Attached you have a picture of the graph (obviously, red is B1 sensor 1 and green is B1 sensor 2).

 

Thanks a lot!

What time period does that plot cover, and was it from a cold start?

What engine type is this?

 

I think it’s 20-30 seconds. I start revving at about a third. I can re-do the test for a longer period if that’s helpful.

It’s 1.4 Petrol (BXW)

Yes, it’s from a cold start.
 

vagcom shows me I’m in an emissions fail mode even after resetting all the codes.

Thanks!

The rear sensor will take quite a bit longer than the front to warm up into a state where it operates correctly, so the constant high part of the curve at the start is probably normal.

See if the slow up/down cycle of sensor 2 continues over longer timescales. 

 

Have you tried to generate a readiness code and age the probes?

 

20 minutes ago, Wino said:

The rear sensor will take quite a bit longer than the front to warm up into a state where it operates correctly, so the constant high part of the curve at the start is probably normal.

See if the slow up/down cycle of sensor 2 continues over longer timescales. 

 

ok, will try at a normal operating temp.

 

Didn’t know about that. I’m just a little amateur :D.

I have googled it and found about it. Will get one and post here as soon as I get home.

3 hours ago, Wino said:

The rear sensor will take quite a bit longer than the front to warm up into a state where it operates correctly, so the constant high part of the curve at the start is probably normal.

See if the slow up/down cycle of sensor 2 continues over longer timescales. 

 

 

3 hours ago, Tech1e said:

Have you tried to generate a readiness code and age the probes?

 

 

 

Readiness test and Youtube link with 4-5 minutes of monitoring the O2 sensor graph.

Whenever you hear the revving that is up to 3-4k. Engine is at 90 C.