I'm getting a 'pending fault' of 'O2 Sensor Circuit Slow Response' (B1S1) and I'm concerned that it could be a warning sign of the catalytic converter going out. Reason I say this is because this CEL code appeared immediately after I replaced the upstream sensor (P0135 'O2 Sensor Heater Circuit' code popped up). It usually goes away after a few days but will pop up randomly mostly at any sign of "aggressive" driving (e.g.- 4k+ RPMS ).

So is it just a coincidence that the secondary sensor has gone out right after the primary or could I possibly have some other issues going on?

Thanks

 

If the CEL appeared right after doing work "X" on the car go back and check work "X". General rule for mechanics. Double check the prior work first.

Utah

 

I would say second o2 sensor was already bad but since the first and second deteriorated and we're not as sensitive as new. I would go ahead and replace the secondary one.