P0420 code

[Ajcanadian]

I recently got a code on my E46 M3, p0420. Not sure if it's a cat code or o2 sensor code. Couldn't find too much info on this. Any help will be appreciated

[SteelGreyM]

I THINK it means your cat(s) is (are) failing. You can either replace it or code it out with ECU work for $26. Someone please verify that my thinking is correct.

[Mike RT4]

I recently got a code on my E46 M3, p0420. Not sure if it's a cat code or o2 sensor code. Couldn't find too much info on this. Any help will be appreciated

Have you changed any aspect of the exhaust system?

[Ajcanadian]

I THINK it means your cat(s) is (are) failing. You can either replace it or code it out with ECU work for $26. Someone please verify that my thinking is correct.

I was thinking about doing the EU2 tune or just buy Megan racing headers.

[Ajcanadian]

Have you changed any aspect of the exhaust system?

I have not. If it helps, I just had the rear subframe reinforced, so my exhaust was out

[Mike RT4]

If the code does not come back immediately on clearing than all it is likely to be is just a disparity between expected and recorded readings between the front and rear O² sensors. This usually happens if the car has high flow cats, a decat or an after market exhaust that can cause a different reading between the two. Catalyst System Efficiency Below Threshold (Bank 1) is usually the error code once investigated. I have known for the code to also appear if the car has been driven lightly (as in cruising at a steady state speed for long periods) with standard cats.

As long as it only comes on infrequently, I wouldn't worry too much. If you do notice a drop-off in performance as well as a rattle from inside the exhaust, then this is when you should worry about the cats falling apart .

I have a full Supersprint system from the headers back on mine (inc high flow cats) and am having to clear the code quite often, which I'd rather do than turn the rear sensors off.

[Ajcanadian]

If the code does not come back immediately on clearing than all it is likely to be is just a disparity between expected and recorded readings between the front and rear O² sensors. This usually happens if the car has high flow cats, a decat or an after market exhaust that can cause a different reading between the two. Catalyst System Efficiency Below Threshold (Bank 1) is usually the error code once investigated. I have known for the code to also appear if the car has been driven lightly (as in cruising at a steady state speed for long periods) with standard cats.

As long as it only comes on infrequently, I wouldn't worry too much. If you do notice a drop-off in performance as well as a rattle from inside the exhaust, then this is when you should worry about the cats falling apart .

I have a full Supersprint system from the headers back on mine (inc high flow cats) and am having to clear the code quite often, which I'd rather do than turn the rear sensors off.

Makes sense, the code did come up right after a small 200 mile highway commute. My car is on stock exhaust (for now)

I'll try to get a different scanner and clear the code. My generic amazon scanner, isn't helpful with clearing the codes. I'll do it using PA soft or Inpa.