[Trollstein]

2016 BMW M235i

Recently DIY installed a Remus racing downpipe with a sport catalytic converter (200 CPS). No CEL, no smells, or audible exhaust leaks initially. Drove for several weeks without issues, but now a check engine light (CEL) is on -- code P0420 - Catalytic Converter Conversion.

Possible culprits:

1. Seal misaligned, causing a slight leak
2. Issue with O2 sensor (although that should trigger a different code, right?)
3. Standard aftermarket downpipe CEL issue

I'm assuming it's #3 - a standard aftermarket issue.

Potential fixes:

1. Clear the code and hope it doesn't return
2. Install an O2 spacer (just found this option, but I really don't want to crawl back under the car and pull the downpipe again)
3. Tuning: On my heavily modded E46 330i, I remember flashing a Euro2 (EU2) tune, which bypassed the entire cat & post-cat O2 system (I could remove the whole secondary air pump system without throwing any codes)
4. Use a JB4 or similar tuning box

My goal:
I'd like the easiest, most cost-effective option to eliminate this CEL (assuming there are no leaks, which I don't think there are). I'm in Minnesota; no emissions testing here!

Current mods (in order of install history):

• M-performance exhaust
• CSF intercooler
• Evolution Racewerks oil cooler
• Active Autowerke charge pipes
• UUC short shift kit
• Dinan lowering springs
• AFE cold air intake
• Painted front lip
• Remus sport cat downpipe
• IND painted reflectors

Estoril blue

Any suggestions or advice on the best approach?

Cheers!

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BMW M235i M-Performance Exhaust + Remus Downpipe Install - Before & After Sound Comparison

[mike@x-ph.com]

your best bet is to get bootmod3

the JB4 does not hide the code

[Trollstein]

Originally Posted by mike@x-ph.com

your best bet is to get bootmod3

the JB4 does not hide the code

Oof, looks like $595 + $99 for the WiFi adapter? Pretty sweet flash tuning setup (I hadn't seen this before), but any cheaper route than that?

Perhaps a custom ECU tune, simply modify the DME to bypass the secondary O2 sensor checks, similar to what I did with the EU2 tune on my ole E46?

[Trollstein]

I found a local guy with a Bimmer Geeks ProTool. Anyone know if this is capable of coding out the emissions checks?

Looks like expert mode in ProTool allows for advanced modifications to nettodata or NCD files. I'm just not sure if this gives access to disable the secondary O2 sensor checks or other emissions-related diagnostics...

[M235SDCA]

BM3 would be your best bet IMO. I believe the only way to remove the CEL is with DME tune and it is not something you can code out. BM3 has a setting where you can suppress that specific code.