P0421 error code on 2013 Mazda CX-5 Sport

I keep getting the P0421 code on my 2013 CX-5, I've had the Cat and both sensors replaced, all the ignition coils and spark plugs, gaskets, seals everything my mechanic can think of. Has anyone experienced this?
 
I keep getting the P0421 code on my 2013 CX5, I've had the Cat and both sensors replaced, all the ignition coils and spark plugs, gaskets, seals everything my mechanic can think of. Has anyone this?
P0421 Code: Warm Up Catalyst Efficiency Below Threshold (Bank 1)

With this code if you have replaced both upstream and downstream oxygen sensors and even catalytic converter, and the CEL still lit up, I believe your mechanic used cheap aftermarket catalytic converter and oxygen sensors which may not work to get rid of CEL. A real effective catalytic converter usually costs over $1,000.

How many miles on your 2013 CX-5?
 
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P0421 Code: Warm Up Catalyst Efficiency Below Threshold (Bank 1)

With this code if you have replaced both upstream and downstream oxygen sensors and even catalytic converter, and the CEL still lit up, I believe your mechanic used cheap aftermarket catalytic converter and oxygen sensors which may not work to get rid of CEL. A real effective catalytic converter usually costs over $1,000.

How many miles on your 2013 CX-5?
152k. this is the CAT that was installed.
 

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Someone suggested it could be the front catalytic converter built into the exhaust manifold.
I really don’t believe CX-5 uses 2 catalytic converters. Usually with P0421 at your 152K miles, you need a new catalytic converter. Unfortunately a quality CC is too expensive, and the cheaper one may not good enough to get rid of the CEL. Oxygen sensors are similar. Inferior sensors may trigger the P0421 too. And Denso oxygen sensors are the ones you want to use. People dump CC cleaner into the fuel tank、submerge entire CC in a bucket of cleaner、replace oxygen sensors、replace catalytic converters (in sequence) and try to get rid of the P0421 but sometimes just at no avail. Like your mechanic I simply don’t know what is the next step you can do other than spend more money with OEM oxygen sensors and OEM catalytic converter which of course would cost you a lot of money but no guarantee.
 
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I really don’t believe CX-5 uses 2 catalytic converters. Usually with P0421 at your 152K miles, you need a new catalytic converter. Unfortunately a quality CC is too expensive, and the cheaper one may not good enough to get rid of the CEL. Oxygen sensors are similar. Inferior sensors may trigger the P0421 too. And Denso oxygen sensors are the ones you want to use. People dumps CC cleaner into the fuel tank、submerge entire CC in a bucket of cleaner、replace oxygen sensors、replace catalytic converters (in sequence) and try to get rid of the P0421 but sometimes just at no avail. Like your mechanic I simply don’t know what is the next step you can do other than spend more money with OEM oxygen sensors and OEM catalytic converter which of course would cost you a lot of money but no guarantee.
I found this article interesting in that it mentions air leaks as a possible cause of the P0421 code. Just throwing it out there.

 
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