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P0300 Code Please Help!

Old 01-26-2007, 02:27 AM
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Join Date: Jan 2007
Posts: 4
Default P0300 Code Please Help!

Hello guys. I am a 1st time user of this site, just found it last night. I was hoping that you could help me with a problem i am having with my 2001 protege es gt with a 2.0 L engine, manual Trans. It has 41500 miles on it, I am the 2nd owner. I bought it when it had 27000 miles on it. It has worked great until a month ago.

I started it one morning to my surprise it was shaking and sputtering and missing something awful. I shut it off and had it towed to mazda, they replaced my egr valve(they said it was stuck open).They sayit had a multi-cylinder misfire code # P0300. I took it home and drove it the next day and it started alright but once i started driving the car, it began to misfire and sputter and it almost stalled.The engine light came on and stayed on so i turned around took it back to mazda. They cleared the code and said they couldn't find anything wrong. I picked it up from the dealer and drove it for a couple of days in the city and it seemed to work but i think it misfired a couple of times but not enough to make the engine light come on. Yesterday i went started it in the morning and it idled really rough again and the engine light came on and stayed on again. Took it to mazda again, while i was driving over there i smelled Rotten Eggs.and again it wasa P0300 multi- cylinder misfire code. So they told me i needed plugs, so i told them to put them in. Started the car up at the dealer to take it home, but the light came on and the service manager came out and hooked up his computer and it was the same code P0300 and i actually witnessed that. So he said that he would put in a claim for new coils, which mazda agreed to and they put new coils in. So i drove it home which is only maybe 10 miles at most but it seemed to work alright. I got home and opened the door and revved up the engine but now i think it is making a funny noise and from what i can figure out is that it is coming from the catalytic converter. It's a sound like tin rubbing tin, like a muffler clamp is loose or something of that type.

I guess my question is, do you think they fixed the problem of misfiring? And is there something they could have done to make the catalytic converter make noise like i described? I am at my wits end with this car.

Please help!
Old 01-26-2007, 03:06 AM
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Join Date: Jul 2005
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Default RE: P0300 Code Please Help!

They may have fixed the missfire problem after several random jabs at things that could create the problem but the question back to you is "Is the engine still feeling like it is missfiring or running rough?" Which catalytic converter do you hear the rattling noise from? The front warm up CAT up near the exhaust manifold area or main CAT under the seating area of the vehicle? Severe missfire concerns can damage a converter very rapidly but should still be covered under emissions warrranty which is 8 years or 80k miles
Old 01-27-2007, 02:51 AM
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Join Date: Jan 2007
Posts: 4
Default RE: P0300 Code Please Help!

Thanks so much for responding.
I heard the noise of the tin on tin from underneath my car. At least that is where i think it was coming from. The car never really acted like it was running rough today but i am so mad that it could have been.

Well they never fixed it because this morning i got 3 blocks from my house and the engine light came on again. So i drove it to the dealer and they looked at it and said that it had a different code this time. I only talked to him on my cell and i was at work so i didnt ask what code but now they say it is my catalyst, which is covered under warranty but will take them 5 days to get one out of the USA(i live in Canada).
So i hope they finally found out what is wrong.
Is the Catalyst the Catalytic Coverter? I am confused about this?
Thanks again for your time and help.
Old 02-02-2007, 05:15 PM
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Join Date: Jan 2007
Posts: 4
Default RE: P0300 Code Please Help!

I just got my car back from mazda again. They have had it for a week and they replaced the front catalytic converter. They said that they got a new code. It was a P0421 and from what i can tell by reading other posts they changed the right part. I am hoping this will finally fix my car. The other code they always got was a P0300 code.

So far they have changed plugs, ignition coils, egr valve, and now the converter.

please comment if you guys think they fixed it.

thanks for your time.
Old 02-02-2007, 10:58 PM
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Join Date: Jul 2005
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Default RE: P0300 Code Please Help!

Unlikely that the catalyticconverter would cause the P0300 random missfire code unless it was plugged up. Probably only time is going to tell if the engine runs rough again and sets the code yet again. Hopefully not.
Old 02-03-2007, 08:27 PM
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Join Date: Jan 2007
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Default RE: P0300 Code Please Help!

thanks for responding, i have not drove it since but will keep you informed on what the outcome is
Old 07-20-2007, 09:41 PM
Join Date: Oct 2005
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Default RE: P0300 Code Please Help!

Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly. A P0300 OBD code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why. It could have been caused by your faulty catalytic converter(s), spark plugs or wires, camshaft position sensor, coil (pack), oxygen sensor(s), fuel injector(s), burned exhaust valve, stuck/blocked EGR valve / passages or a defective computer.. The symptoms for this code is that the engine may be harder to start or may stumble / stumble, and/or hesitate, but other symptoms may also be present... If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). There is also the possibilty that your Mazda catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors. Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.
Old 07-26-2007, 01:46 PM
Join Date: Jul 2007
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Default RE: P0300 Code Please Help!

My 2003 protege just did the exact same thing. The Dealer replaced the EGR, but that didn't help. He then replaced one of the coils. It runs fine now, but 1 day later the check engine light came back on. The code was P0421. I checked the front O2 sensor (.2 to .8 V), it seems fine. My next guess is the cat converter. My car has 92,000 miles, so I guess the converter is not under warrenty anymore.

The car drives fine. Does anyone know if it is bad to just keep driving it with a bad converter? Do junk yards sell converters?

Old 07-31-2007, 12:26 AM
Join Date: Jun 2007
Posts: 8
Default RE: P0300 Code Please Help!

unfortunately i have this happen to me. it started with the coil misfiring and i had the exact same symptoms of a sputtering engine that sounds like a lawn mower. i replaced the spark plugs first but that was no good and i then hoped that it would be the ignition coils, so i ordered them and that fixed that problem. i then got the PO421 code, and from what i've noticed in several forums, once you get the miss-firing code, the PO421 code comes right after, i am just guessing but i think this is related somehow. now for the PO421 code, i tried fixing it by trying to replace the cheapest parts which were the 2 O2 sensors, however that didnt work and it ended being the pre-cat. now that CEL is gone.
Old 01-02-2008, 07:27 PM
Join Date: Jan 2008
Posts: 1
Default RE: P0300 Code Please Help!

I have an '01 Protege & I've been having the same P0300 code with the same symptoms as you originally described. I don't have a Mazda dealer with a shop in my town but my personal mechanic has gone through everything trying to fix this problem. We both thought it might be bad gas, but several bottles of HEAT & a gas sample proved not to be the case. He's gone through all of the fuel system & find it to be in good working order. He replaced the spark plugs & made sure the EGR wasn't the problem. Now he says we should replace the coils & wires 'cause he thinks that will fix it. I've all ready sunk several hundred dollars into trying to fix this problem & nothing has worked yet. Before I go sinking a couple more hundred into this coils & wires idea, I'd like to hear if anyone has for sure gotten this problem fixed & how they accomplished it. Please.

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