[SOLVED] How do I avoid a CEL with a catless DP?

Just installed my turboxs catless downpipe and racepipe on my 09 gen 1 speed3. It sounds awesome. However, roughly 30 miles after the install, 3 miles into the third drive after the install (which I didn’t let it sit and warm up because I had to get somewhere), it threw a CEL with a P0421 code.

Some guys use anti foulers for spark plugs, others just modify the second o2 sensor.

What is the best way to get rid of the CEL for the catless dp? I want my CEL to work for everything else still, so electrical tape isn’t an option lol.

Thanks!!

 

You need a tune for that dp or you are going to overboost your engine and blow itt

 

Thanks for letting me know, I already thought I needed a tune but that confirms my suspicions. I am getting tuned by freektune as we speak, I made sure to already have the first map of his OTS+ map on my car before driving it. However, he will be sending me at least one more revision so maybe after that the CEL won’t be so prevalent?

 

If you are using an access port you can't turn it off

 

I know I can’t tune it out. I’m asking if there’s a solid way to not cause the code to be thrown in the first place. Could I use an o2 sensor bung extension to get a content reading on the second o2 sensor?

 

Oh, in that case



No

 

So then I’m just screwed? Surely there’s a way to eliminate the issue…can I modify the sensor to make it always read correctly?

 

I'll refer your back to the same answer;

Pesky recent update from cobb

 

Hmmm, ok. So even the options in this post https://www.mazda3forums.com/threads/catless-cel-fix.314582/ aren’t valid?

 

No

 

As dead set as you both seemed on there being absolutely nothing I could do, I tried a Vibrant performance J-style spacer and an exhaust reducer and my check engine light has been gone since. So, If you have a first gen mazdaspeed3 try a j spacer out. It does the trick.

Here is where I got mine: https://fasthemis.com/i-23894159-vi...-degree-w-adjustable-jets-cel-eliminator.html

 

Your cel is gone for now

Report back in a few months

 

Bunny can you explain this further?

Ive always been curious about this and I have no interest in a catless DP. I have a Cobb catted I'm going to put on the car in the spring and retune.

Obviously the ECU is comparing values between the primary and secondary O2 to discern Cat efficiency. What is it about the ECU logic that will not allow you to fool the system by limiting the exposure to exhaust stream on the secondary 02?

 

You should start a separate thread on your question. You could get a lot of posts not pertaining to this one's title. In simple terms the ecu is a closed-loop controller; it creates a decision on one end of the controlled device (air+ fuel mixture) at the other side of control device it measures the results. The results had better match the ecu programmed expected response. The controller can fine tune with the two outputs on exhaust sensors to see catalytic efficiency. Depending on requirements in certification (CA has different requirements) the manufacturer can then sell it in USA. That's why the option of delete cel is being taken away by Cobb and Likely Versatune (I get ecu updates it seems weekly for latest Mazda tunes...
Not my 06,07,08 speeds Please!
Hopefully completely removing owners/tuners ability to modify anything in ecu is way down the road. I am happy the poster has his solution. I know in California it would fail the simple eyeball visual test which is a requirement.

 

Reporting back a few months later. My CEL is still gone, hasn’t appeared once. Unless there’s some software glitch with the ecu, this is working for my setup.

 

Hey, I have a question I’m going to use the same spacer on a 2010 GEN 2 speed3, have you heard of anybody have any luck with it working like it did for you on the GEN one let me know please and thank you

 

I've heard of the odd one working on gen 1 but I have yet to hear if one working on gen 2 as there is a slight difference in logic between the ecus of I recall correctly. Would not recommend

 

I cannot confirm nor deny this working for your application unfortunately.

To the best of my knowledge, the gen 2 logic is different as Awafrican stated. That being said, if there was a trick to remove the CEL, this would be the way to make it work. You could try using the smaller restriction bottleneck when using it, that may work.

 

Gen 1/ms6 ecu logic is different. Both my gen 1 and ms6 have run catless downpipe for over 250k miles combined and have never thrown a p0421 or any cat efficiency codes, neither have either been modified as to sensor placement or any modified bugs. My ms6 has a kozmic downpipe and my ms3 had an ultimate racing stock flange downpipe, then was replaced by a custom PTE vband downpipe pipe.

Gen 2's are known to throw a p0421 even with a high flow catted downpipe. Especially when ambient Temps are below 50°F