P0421 at 40k miles??

D

dailygasfillups

Member
:
2015 CX-5
I've searched and searched, but couldn't find an answer on two things occurring with my CX-5.

It just hit 40k miles about a week ago and it has, just today, given me a CEL. I stuck my OBDII reader and it gave me P0421. Could it already be a faulty cat? Or should I replace the something, or do other checks before taking it to a shop? I have never seen a P0421 on a car with such few miles, and I would hate to have to dump a couple hundred into a car that isn't even that old.

Secondly, the engine makes a very strange rumbling (or vibrating?) noise under load. Accelerating on the on ramp is where I can hear it most, and I cannot find another user with the same problem, or even a solution. The thing is, if I put the car in neutral and rev the engine, it won't make any noise, so I can pinpoint the location of the problem. All fluids are fine, and nothing running low.


Any help would be appreciated on either problems. Thanks!
 
I checked the Mazda codes and there are several things that can throw that code including 02 sensors, loose electrical connections along with the Cat. Could be nothing more than a slow reacting 02 sensor or connection. I think all the sensors and the CAT fall under the emission warranty of 70,000 miles? The second problem is probably caused by the first. Ed
 
If it is the cat don't worry - it will be covered under emissions. I had the cat go in my Maxima at around 72k and Nissan still covered it completely.
 
dailygasfillups said:
I've searched and searched, but couldn't find an answer on two things occurring with my CX-5.

It just hit 40k miles about a week ago and it has, just today, given me a CEL. I stuck my OBDII reader and it gave me P0421. Could it already be a faulty cat? Or should I replace the something, or do other checks before taking it to a shop? I have never seen a P0421 on a car with such few miles, and I would hate to have to dump a couple hundred into a car that isn't even that old.

Secondly, the engine makes a very strange rumbling (or vibrating?) noise under load. Accelerating on the on ramp is where I can hear it most, and I cannot find another user with the same problem, or even a solution. The thing is, if I put the car in neutral and rev the engine, it won't make any noise, so I can pinpoint the location of the problem. All fluids are fine, and nothing running low.


Any help would be appreciated on either problems. Thanks!
Click to expand...

You mean like a miss or running rough? If so, could be causing the cat to throw a code. Maybe a bad coil, plug, wire, etc. You could throw a bunch of parts at it or just take it back to Mazda and be done with it. If it's anything emissions related it should be covered under warranty. I don't how much coverage your power train warranty (I'm guessing you still have some left) will offer here. Probably an O2 sensor.
 
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What were the circumstances? I could get my Speed 3 to show a PO421 by just idling around a residential neighborhood in 2nd gear after initial start-up. The cat isn't warming up according to the ECU's desires. Ain't no big deal.
 
well, thats definitely not normal at your mileage.

are you experiencing any sort of oil consumption?
 
1. I guess I'll take it to Mazda to see what they have to say about it.

2. The "rumbling" was probably a bad way to describe it. You don't feel anything, nor is it that noticeable. I guess it's more of a clicking noise. Doesn't seem to affect the power or mileage at all. Nothing really wrong with it except for the noise.
 
dailygasfillups said:
1. I guess I'll take it to Mazda to see what they have to say about it.

2. The "rumbling" was probably a bad way to describe it. You don't feel anything, nor is it that noticeable. I guess it's more of a clicking noise. Doesn't seem to affect the power or mileage at all. Nothing really wrong with it except for the noise.
Click to expand...

Definitely take it to Mazda and get the code and mileage written down on some official paperwork.

That way, if the code ever returns at a higher millage it will be covered by warranty.
 
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