I did a valve cover gasket, spark plugs, and coils on 2017 Mazda 6. It's the 2.5 liter engine. I then added some B-12 chemtool now I'm getting a troublecode P0421 which idles rough. Can someone help me with this problem please? It been at least two weeks and I just can't seem to get it right. My guess is the oxygen sensor before the cat....
2017 Mazda 6 doesn't run properly
- Thread starter jmpsr79
- Start date
Moved to mechanical
P0412 is catalytic converter code, check for vacuum leaks and any items that you unplug like the MAP sensor.
I suspect a vacuum leak as well. A hose that you disconnected wasn’t reconnected properly, or broke when it was reconnected. It ran OK before your work, so, I suspect your work disturbed something.
Or, you have fake parts. Where did you get your spark plugs and coils?
Or, you have fake parts. Where did you get your spark plugs and coils?
I agree to recheck the parts you installed.
Also...
I had a Lexus RX300 that did not like fuel system cleaners. Every time I added a FSC, a CEL would appear in the dash(petering to AF ratio or O2 sensors) until that tank of fuel was gone and replaced with fresh fuel from the next tank. SO I stopped adding FSC's to the gas tank.
Also...
I had a Lexus RX300 that did not like fuel system cleaners. Every time I added a FSC, a CEL would appear in the dash(petering to AF ratio or O2 sensors) until that tank of fuel was gone and replaced with fresh fuel from the next tank. SO I stopped adding FSC's to the gas tank.
Oreily
You added a fuel additive to your gas tank and now think it caused a fault? Right after you did a decent amount of work on the car? Swallow your pride here and accept that something went wrong during that work.
FWIW....I ran an STP intake valve cleaner through our CX-30's 2.5 and it caused a similar issue....it even lost power (as if it were in 'limp mode'). I disconnected the battery for a few minutes and when I reconnected it the issue went away. IDK if this will work for you but it's worth a try.
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If everything was fine before hand, like said above, start by re-tracing your steps of everything you touched and disconnected. I would think your O'Reily parts would throw misfire codes if it was them, but I wouldn't trust aftermarket coils unless they were re-boxed OEMs.
I'm not familiar with this particular P0421 code "warm up catalyst efficiency below threshold". I am assuming it's the same as the standard 420 "catalyst inefficiency" codes.
I'm not familiar with this particular P0421 code "warm up catalyst efficiency below threshold". I am assuming it's the same as the standard 420 "catalyst inefficiency" codes.
This
If things are worse than before the work, check for missed reconnections or cracked hoses.
If all that looks good, start backing out the changes you can such as the coils and plugs.
Re-evaluate at each step.
This is why I would have never done all of this at once. Had you waited to do the B-12 chemtool you would have known for sure if that was it,
P0421 is an odd one. Its signaling bad efficiency only during warm up?
Are you also getting a pending code for P0420?
I would suspect either a latent misfire from the plug / coil change, or you gummed up the cat. If it were me I would scan for latent misfires - they would show up in the PID's and you can find them with Torque Pro for cheap or a higher end dedicated scanner.
If you don't have any amount of misfires I would guess you gummed up the cat somehow. Could have been the Berryman - junk from the upper end got cleaned out and blown into the cat?
Are you also getting a pending code for P0420?
I would suspect either a latent misfire from the plug / coil change, or you gummed up the cat. If it were me I would scan for latent misfires - they would show up in the PID's and you can find them with Torque Pro for cheap or a higher end dedicated scanner.
If you don't have any amount of misfires I would guess you gummed up the cat somehow. Could have been the Berryman - junk from the upper end got cleaned out and blown into the cat?
Heater in the downstream O2 sensor went bad (slow to heat up and get accurate?)
Cat slowly going bad?
Is it running ok otherwise?
Chemtool somehow slows the warmup of the Cat?
Cat slowly going bad?
Is it running ok otherwise?
Chemtool somehow slows the warmup of the Cat?
+1
That's how I generally avoid mishaps.
Don't get me wrong, I've made terrible mistakes in the past, but I've learnt to only do one thing at a time.
Hopefully, just needs an idle learn reset. As mentioned, try disconnecting the battery for a few minutes. Start back up and let idle for 10 minutes. Clean throttle body also before the idle re-learn if that hasn't been done recently.
I had a cracked boot a while ago on a plug change. It didn't show up as a misfire, but I could feel it at times, and it showed up on the extended PID's - but not enough times to throw even a pending code.
So basically I agree with you on the O'Reilly coils as being a possible fault.
Change one thing at a time.
Yes boots always a concern! And if you kinda know what you're looking for you can sometimes spot carbon tracking on the exterior.
Still, absent ANY ignition related codes or misfire counts greater than zero, I wouldn't necessarily chase coils and boots FIRST, esp since OP did a bunch of work just prior.
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