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P0421

Posted: Mon Sep 18, 2023 4:36 pm
by AlbertoC215
Hi there,
I was getting this code (P0421) on my 2015 club with 39,000 miles. It has a RoadsterSport All Stainless Steel MX5 COMPLETE STREET EXHAUST COMBO...with CERAMIC installed @ 18,000 miles. I replaced both sensors with OEM parts and it was okay for 10 days. Today the "magic" light turns on again... It's no way the catalytic is bad... it's only 20,000 miles old???
Any clue?

Re: P0421

Posted: Wed Sep 20, 2023 7:47 am
by Brian
Likely a sensor connection. Look at the pins in the plugs for the O2 sensors, are all the pins flush or did one get pushed deep inside the plug?

Re: P0421

Posted: Wed Sep 20, 2023 8:06 am
by AlbertoC215
Thanks Brian, I will check the connector...
Al

Re: P0421

Posted: Thu Nov 02, 2023 4:01 pm
by AlbertoC215
Hi Brian,
This weekend I could check the plugs..., they were fine. Then I cleared the code. But after running a few miles the engine light turns on again, same code... Any idea?
Let me know. Thanks.
Al

Re: P0421

Posted: Wed Nov 08, 2023 10:48 am
by Ryan @ GWR
Hi Al,

The code will keep coming back until you find the actual cause of the issue.
Check the wiring as well. Sometimes a zip tie comes loose or similar and the wire gets melted against the exhaust.
If all the wiring for the sensor is good, the connector is good, and you've replaced the o2 sensors, then the cat itself is the next suspect.
Get in touch with us by email and we can help further.