Flashing CEL - P0300 & P0421 - 2001 2.0 ES

[adrocking]

Looking for a little advice or ideas.

I have a bone stock 2001 ES 2.0 and about two weeks ago I got a flashing CEL. Ran the code and got back a P0300 for a random misfire and P0421 for low cat threshold.

After trying the things below I still get a flashing CEL about once every other day, so if you have any suggestions please let me know.

Things done thus far:

Cleaned EGR Valve
Replaced both front and rear (up and down) O2 sensors
Changed plugs
Bench test coils and wires, which came back fine
Inspected the Cat, looks to be fine

[Wykydtron]

I'll ask at work tomorrow what the mechanics think you could do (work at a Mazda dealer). They hate it when that code comes up because there's the possibility of so many other things other than 'random misfire'

[adrocking]

thanks man.

[Wykydtron]

He said that it could most likely be the EGR since you checked the coils. There's actually a bulletin for the EGR for the protege. Get the dealership to run your vin, there's a chance it's still under warranty.

[adrocking]

thanks for the help.

[mp3driver01]

Looking for a little advice or ideas.

I have a bone stock 2001 ES 2.0 and about two weeks ago I got a flashing CEL. Ran the code and got back a P0300 for a random misfire and P0421 for low cat threshold.

After trying the things below I still get a flashing CEL about once every other day, so if you have any suggestions please let me know.

Things done thus far:

Cleaned EGR Valve
Replaced both front and rear (up and down) O2 sensors
Changed plugs
Bench test coils and wires, which came back fine
Inspected the Cat, looks to be fine

my mp3 did this except it was just a coil pack going bad. i had to keep coil pack with me and change them when it happened and then drive it and see if happened again, eventually i found the coil pack or hell just replace both of them there only like 30 bucks a peice new.

[Markmitsu]

Hi i'm having the same issue. Could you please post the resolution when you know? thanks!

[ghettoracingkid]

ok i had the same issues. herei s what you do.

change the plus, coil packs (autozone has them for like $18 a pop) and the wires. also run some seafoam threw the gas and the intake (so a search for seafoam.) It will clear up the problem.

[25FConv]

Before spending money just throwing parts at the car...doesn't really make sense to replace parts that aren't messed up..check each piece like adrocking did. 3rd gen proteges are notorious for having an EGR issue to where the pin that opens and closes the valve breaks leaving it closed or halfway open and closed at all times. which will give you both of those CEL lights.

[MAKRAA]

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...

[LeeC]

Makraa - did you replace the egr valve? You put in your post EGR kit. I'm also having similar problem that has just started. I get a slight buck at acceleration and the cel code P 0421 comes on after about 125 miles. I have determined that my issue is the EGR valve.

[MAKRAA]

Yes the valve was replaced at the time the ERG kit was updated says my receipt :)

[eromaes]

i have the p0421 code right now also i just replaced the whole engine with an engine that has 65k on it so im guessing its the cat because everything else was replaced after new engine put in ex.( new plugs, coil packs, wires, egr was fine did not need new one).. so my guess is the cat for me.. not sure if anyone else has a say at it?

[MAKRAA]

I've already replaced the front cat so I got the second cat to go yet...