Hi, okay so I bought this vehicle brand new, 13 miles on this baby. It has served me well with routine maintenance. Recently, I came to a stop light and as i sat there the car started sputtering like it was going to run out of gas. After I put fuel in the car drove alright for about 5 blocks and began sputtering again and this time the CEL came on. Drove straight home, the next day as I drove to work the CEL came on and started flashing and the car began sputtering and lost power. Drove it home and parked it, after driving like this for a few days finally took it into Tires Plus and they said it was P0300 code and my wires and spark plugs were shot. Got those changed yesterday and guess what, it started flashing again, my boyfriend check the code and it came back as a PO421. So my question, after reading this forum, is what do I check next, the EGR, the 02 or the pre-cat.
TIA

 

P0421 is a warm up catalyst efficiency error.

Go to this link and look at page 71
http://protege5.ugly.net/01-02a.PDF

It could be the cat or the sensors, but, with the symptons you describe, I think the CAT is blocked...

 

Just to clarify, the sensor is an O2 (Oxygen) sensor, not a 02 sensor.

By the way, I've been reading a lot on this forum about people with bad/clogged cats or pre-cats. Any idea what causes pre-cats or cats to get clogged or otherwise go bad? Anything a person can do to prevent these problems? Just trying to get some insight.
[align=left] [/align]

 

Use high quality gasoline. 89 octane or better, and keep your car properly tuned up.

 

whew, for a moment thought the dealership where I had bought this car had programmed something in it for when I made my last payment, which was 2 months ago.Final payment, BAM, something gives out!?! Just a thought, Well my boyfriend is going to check the EGR this weekend, hopefully we find whats wrong soon as hitching a ride to work is getting OLD already.