Hi who ever sees this. </P>


I got my 99 galant about a year or 1 1/2 ago (it just reached about 90k this wed), and needless to say overall besides me doin some body work due to snow, everythings been ok. Now I dont know much about cars, so if u do reply to this, plz understand im just beginin and may be a lil lost. Now 2 weeks ago when puttin on a replacement hood, the day before i noticed my check engine light came on. To calm my nerves and basically take it off my mind, we just dis connected the battery and boom everything was ok. Well at least till this morn. The light came back on so i went to an autozone to see what code they could come up with. They showed me Warm-Up Catalyst Efficiency below threshold (Bank 1) P0421. Now ive been tryin to search this out and so far i understand it goes with the air flow...but my ? is what do i do to fix this! I commute practically everyday and im still fixin my car from an accident that pretty much only touched the body....so i dont wanna waste money on something i dont need to. If you have any ideas or answers plz reply here or email me at PoconosKel@hotmail.com Thanks in advance</P>

 

i own 2 mitsubishis, a 94 3kgt and a 99 eclipse. Both have had no mods and the check engine lights have been on for years. Nothing shows on diagnosis tests

 

It sounds somewhat like a faultyEGR valve or system. The EGR system is designed to help the engine warm up quicker during cold mornings or cold starts. It basically takes Exhaust gasses that have already passed through the catalytic converter and recirculates it into the intake, usually at the intake manifold. The intake manifold is a big shiny aluminum thing that has a big plenum and six individual little runners coming off of it and leading to the top of the engine. If you know where you're air filter is, just follow the black plastic hose conected to air flter box and you'll eventually come to the intake manifold. It will have a bunch of small hoses and stuff leading off it. Now the EGR Valve is on the Intake mainfold, so you may just need a manual or friend who knows a little about cars to come help you. I don't really know how to check the EGR valve, you will probably be able to look it up on the internet and find a way to do it at home. Now it could be the valve, or it could be a clogged EGR hose. You can clean outthe hoses out with some brake cleaner or engine cleaner, just make sure they are dry before installing them back on. Honestly, your best chance of solving the problem is taking it to a mechanic. They will pinpoint the cause and fix it for you. Also, unplugging the ecu does no good. The problem is still there, and the sensor is still telling the ecu that it has a problem, however the ecu is on it's "learning curve" and will ignore th sensor for a little while. Sometimes days, sometimes weeks. Unplugging the ECU will not erase the prolem or reset the sensors. The ECU only gathers auxilary information, it doesn't control it. Hopefully some of this helps and you cure the problem, if not then just take it to a mechanic. Good luck.

 

That code can also mean something is up with the thermostat...If it isn't working correctly it can cause the engine to stay cold or warm too long.