2009 R56 Base

Replaced upstream and downstream O2 Sensors with Bosch.

Getting recurrent P0420 code before and after replacing downstream sensor. Just got a P0136 after replacing the downstream sensor.

Has anyone had any luck with Catalytic converter cleaner? if so, which one?

Has anyone used a downstream O2 spacer with any success?

I do suspect I have a weak coil pack or two, but am not currently throwing misfire codes. I do have an occasional skip under load.

Only want to replace cat as a last resort.

Thanks!!

Update! Turns out the P0136 was my fault as I didn't have the downstream O2 connector properly connected. it's an unusual connector and if not properly joined, there will be no electrical contact.

 

Since both those codes relate to the post-cat O2 sensor, P0136 specifically, I would be tempted to replace the post cat sensor. However, since you already have done that, might want to check the wiring harness and connection.

 

Yes, I'm definitely going to check the connection.

I was not getting the p0136 before I replace the sensor, so it is logical to check the harness and connection.

I'm just looking to head and if the p0420 keeps coming back, I'm looking for a solution that won't require that I change the cat.

If it gets to the point that I'm on the verge of changing it anyway, it would seem that using catalytic converter cleaner would make sense to at least try.

I'm sure there must be people here that have tried it. Really curious about what the results were .
Same question about the sensor spacer

 

What brand was the replacement downstream sensor? Mini may not be very happy with some aftermarket brands.

I also believe that a functional downstream O2 sensor is required for the DME to throw a bad cat code.

 

Bosch is the OE for the upstream sensor; NTK is the OE for the downstream sensor. You need to perform an oxygen storage test on the converter. If you do replace the cat, make sure it's a MINI cat; aftermarket cats may work for a short period of time, but will fail rapidly.

 

Again, has anyone had any experience with products such as cataclean to clear a P0420?