Error codes p0300 and p0421 Please help

I am new and I am sure this has been covered but I could use some wisdom here. I have these to error codes p0300 Random / Multiple Cylinder Misfire and p0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)

I have replaced my spark plugs with Autolite Platinum. when I got the p0300 error code. the error code went off before I changed the plugs and now they are changed the CEL is still on and sometimes is flashing. what it feels like is that car is bogging and running on maybe two cylinders and has a rough idle to where it almost dies. So I dont think the prob is spark plugs because it was doing it before I changed them and is still doing it.

Oh also my car is the 2.0 and it has 83500 miles on it, I am horrible at doing maintance and usually wait till it gets really bad to fix stuff.

One other thing on side note I changed my front struts and now I have a really bad shake going on pretty much at all speeds. I have taken it to a local tire shop to check the alignment and thats good and checked the balance on the tire and that was good I also had them check to see if the rim was bent and its not. Any ideas?

I really love this car and have never had issues with it and I know that this is standard maint that should have prob been done a while ago.

Thanks in advance

Brad

02 Protege ES said:

I am new and I am sure this has been covered but I could use some wisdom here. I have these to error codes p0300 Random / Multiple Cylinder Misfire and p0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)

I have replaced my spark plugs with Autolite Platinum. when I got the p0300 error code. the error code went off before I changed the plugs and now they are changed the CEL is still on and sometimes is flashing. what it feels like is that car is bogging and running on maybe two cylinders and has a rough idle to where it almost dies. So I dont think the prob is spark plugs because it was doing it before I changed them and is still doing it.

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Well, FWIW, Platinum spark plugs aren't best in these motors.

But chances are that you either have a bad spark plug wire, or a bad ignition coil. Check/replace those.

Oh also my car is the 2.0 and it has 83500 miles on it, I am horrible at doing maintance and usually wait till it gets really bad to fix stuff.

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:'(

One other thing on side note I changed my front struts and now I have a really bad shake going on pretty much at all speeds. I have taken it to a local tire shop to check the alignment and thats good and checked the balance on the tire and that was good I also had them check to see if the rim was bent and its not. Any ideas?

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Take it to another place. Chances are, either a wheel/tire is out of balance, or your alignment is off, or you have some damaged suspension component.

Is there a way to check the coil? where do you recomend buy the coil and or plugs from?

When i changed the strut everything down there looked good but ill take it to Les Schwab and see what they say

Thanks

DO NOT by any means drive the vehicle with a flashing CEL....

I had the p0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1) come up on my 2001 2.0 LX at the end of September. According to the mechanic I normally I take my car to and the Mazda dealership who verified the code, it means that the catalytic converter on your car is on its way out. What stinks is that your car had 83500 miles on it when that particular code came up. The emissions warranty straight from Mazda on the catalytic converter is 96 months/80,000 miles.

B1GHAM said:

DO NOT by any means drive the vehicle with a flashing CEL....

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I've done it because I had no other choice, had to get to work :'( it was not fun at all, I'll never do it again!

I had really bad wires, two cylinders were misfiring like crazy

02 Protege ES said:

p0300 Random / Multiple Cylinder Misfire and p0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)

One other thing on side note I changed my front struts and now I have a really bad shake going on pretty much at all speeds. I have taken it to a local tire shop to check the alignment and thats good and checked the balance on the tire and that was good I also had them check to see if the rim was bent and its not. Any ideas?

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Just posted this in the P5 section.

What cylinder is misfiring?

Switch the ignition coils and see if the misfire moves to another cylinder. If so it is your ignition coil.


Plugs: http://www.mazdas247.com/forum/showthread.php?t=123619931

Misfire threads:
http://www.mazdas247.com/forum/showthread.php?t=123647370
http://www.mazdas247.com/forum/showthread.php?t=123614937

Ignition coils run for $12 - $100 depending on where you go.

I paid $16 and now they are $12, have had no problems. Bought a pair. I have a 5% off discount code also. Hit me up on pm. http://www.rockauto.com/catalog/x,carcode,1387447,parttype,7060





Also, your P0421 is either O2 sensor or cat. Mine was both adn I got a Tsudo header and nonfouler fix.

Take your car in to a reputable alignment shop. Make sure taht all of your blots are tight and your wheel is on tight. I replaced my brakes and torqued the lugs down. Two days later one was loose. I had a bad shake and pulled over and sure enough. Be sure to check your lugs.

Andy2010 said:

I had the p0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1) come up on my 2001 2.0 LX at the end of September. According to the mechanic I normally I take my car to and the Mazda dealership who verified the code, it means that the catalytic converter on your car is on its way out. What stinks is that your car had 83500 miles on it when that particular code came up. The emissions warranty straight from Mazda on the catalytic converter is 96 months/80,000 miles.

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What (if anything) did Mazda do with the CEL code and your cat? My MP3 (with 77k) is throwing the same two codes.

Bob

Hey guys, does anyone know how long the backorder for the coils are for the protege? its a says a 25 day backorder. Does this happen often? I looked all over the place and this is the only place i found that sells ignition coils for cheap. but i don't want to have to wait 25 days for ignition coils. can anyone shed some info on this?

andyman4lyfee said:

Hey guys, does anyone know how long the backorder for the coils are for the protege? its a says a 25 day backorder. Does this happen often? I looked all over the place and this is the only place i found that sells ignition coils for cheap. but i don't want to have to wait 25 days for ignition coils. can anyone shed some info on this?

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i have a set of ignition coils on ebay right now

stores.ebay.com/protegegarage

BondoBob said:

What (if anything) did Mazda do with the CEL code and your cat? My MP3 (with 77k) is throwing the same two codes.

Bob

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Guess you didn't read the post above you.

The Cat code is either the Pre Cat O2 sensor or the Cat itself. You won't know if it is the cat until you replace the sensor and the code comes back.

(glare)

Bob,
The Mazda dealership replaced the catalytic conveter under warranty, which would have cost me just over a grand otherwise. I also had the coil replaced, which was the cause of the random misfire, and a tune-up done.

Andy

I have hadthese two codes on my 2002 mp5 since oct 2009
I have replaced the spark plugs, wires, 02 sensors x2, the ERG kit, catylictic converter, coil packs have been tested, ran many bottles of fuel injecotor cleaner though it. It has been into multiple mazda and private shops plus I have worked on it myself. my problem used to be every couple weeks to months always at about 60 km/h it would lose power almost stall, the engine light would flash for a couple seconds it would suck a bit of gas, then it would go solid and run fine and the engine light would clear itself. Now almost a year and a half later and alot of money and work later it has hugely deteriorated, The engine light is always on solid, it has fits of no power and flashing that can last several minutes, it throws the codes at any speed even in idle it runs terribly and I only get about 300-400 km a tank. I hate the car, I still owe on the car, I am a student with no money to fix or replace the car anymore but am looking at getting a loan to do so but am starting to feel that replacing the vehicle is my only option...

I dont know much about cars, but struts(which you've done), the sway bars, the links on the sway bar, wheel barrings and rear calipers on these cars are notorious for going on the 2002 MP5's, if any of these cause the car to shake look into whether any of these are going in your vehicle.

I have been fighting this issue since late last year. Done most of the repairs referenced here and still have the light, loss of power, etc. Finally replaced fuel pump last week and, viola, no p0300, no power loss, no more issues there. Still have the p0421 code. Think the misfires probably hurt the pre cat. I just wanted to post my resolution as it seems many others have been in the same boat. Used to absolutely love this car, but not so much anymore.

Flashing cel came back today, two weeks after fuel pump replacement. So, guess this wasn't really the fix.

I'm assisting a friend with 2002 Protege ES 2.0, 96K, automatic, and has the same codes on a continuous service engine light (no flashing). This most of 2011 and 2012 winter, at startup ran very rough 1/2 the time and would bog off the line. At 50+ MPH ran unreliably and would die and need a tow, then would start OK next day. It also seemed to be related to cold weather and maybe condensation in tank. Here's how it got better:

A local shop diag'd the car in March. They did a tune and a new Cat were put in before I got to it and this helped some. Now it's warm and I ran 2 tanks with injector cleaner and Marvel Mystery Oil (added to lube the pump and injectors). I suspected the aftermarket Cat needed a burn-in period, so I cleared the trouble codes when it ran better to see if the cure was good. I took the car on 2 x 10 mile drives with 2 shut downs/restarts, various roads and speeds and hills to reteach the computer and get the injectors a chance to get full open and closed. This proceedure seemed to work OK this month and car is improved considerably. No new codes yet.

Note: The 2 different auto parts store guys running the codes both independently suggested that, since the Cat was new, the O2 sensor after the Cat was the most likely cause for the P0421 and said it is as possible that the P0300 came from the bad sensor data leaning the injectors as easily as the injectors being fouled. The injector cleaner and Marvel treatment had a fair chance of cleaning the O2 as well as the injectors, hence my intuition for the computer reset after the Cat burn-in. Hope this helps some one.(thought)

Currently, I would like to know the correct idle RPM for an auto trans 2.0 (2002 Protege ES). I have no book and this simple spec isn't anywhere on the web or 3 forums in the last 2 hour's search. The 2.0 is just a touch rough on initial throttle application from rest. It idles at 750 RPM and sits at 700 RPM in gear warmed up. I think it could use 50-100 RPM at rest to resolve this. Thanks for responses!

is the pre-cat the one front or rear cat?

jneff said:

is the pre-cat the one front or rear cat?

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Pre cat is bolted to your exhaust manifold. Looks like a giant cylinder.