[J-Pizzle]

Greetings forum members; I recently obtained a new to me 2018 M2 6-speed that has had a few mods on it: Dinan cold air intake, exhaust, free-flow cat and Stage 1 mapping. While I am not new to BMWs, I am new to modifications so need some assistance ramping on aftermarket parts.

Unfortunately, I ran into a fault code recently: P0420 Catalyst System Efficiency Below Threshold.

Has anyone run into this before? It states that the cat is underperforming and should be replaced, but I am wondering if it is not optimized for the mods? Any troubleshooting techniques that you would suggest? There is only 15k miles on the vehicle.

I was searching around the forum but did not see anything immediate relevant.

My other vehicles include a F80 2018 M3 6-speed and a F97 2020 X3M, but this little car is amazingly fun to drive and the mods really make a difference from stock.

Thx in advance.

[DanG]

The cat has a. 7 year 100,000 warranty. I would take it to a dealer and make it their problem.

[McGary911]

Originally Posted by DanG

The cat has a. 7 year 100,000 warranty. I would take it to a dealer and make it their problem.

Sounds like an aftermarket cat, so not the dealers problem.

I’d reset the fault and see if it comes right back. If so the issue is likely real.

Who made the free flow cat? They may warranty it. Some aftermarket cats are known to cause these faults out of the box.

I’ve had a fabspeed for years. No lights or issues.

[J-Pizzle]

Thanks for your suggestion, and was heading down that route. I am in the process of trying to figure out the manufacturer. Unfortunately the last owner did not know the brand. He did include the original OEM cat with the sale of the car, so I do have that as a backup.

Since I am new to aftermarket parts, I am in the process of researching an OBD tool to reset fault codes. If you have a recommendation on that front I would appreciate it.

Originally Posted by McGary911

Sounds like an aftermarket cat, so not the dealers problem.

I’d reset the fault and see if it comes right back. If so the issue is likely real.

Who made the free flow cat? They may warranty it. Some aftermarket cats are known to cause these faults out of the box.

I’ve had a fabspeed for years. No lights or issues.

[J-Pizzle]

As a follow-up to my post I was able to reset the fault code and MIL is now off. I performed this just this past monday and the MIL has not returned. I will keep monitoring it.

As an aside, I did notice that the fault code still appears in the "Permanent" section of the OBD scan tool. Once you receive a fault like this it remains in the "history" of the vehicle for all time? I assume there is no way to completely remove any trace of the fault?

[DanG]

Off topic, I noticed that you are local. You should join us at Cars and Coffee at the Shop on Sunday. Here is the link to the event: https://bmw-club-psr.org/events/2023...e-at-the-shop/