okay...so my check engine light is back on! Took the car to Advanced Auto Parts and got a diagnostic reading. The DTCcodes that came back are:

P0421
Warm Up Catalyst
Below Threshold
(Bank 1)

P0431
Warm Up Catalyst
Below Threshold
(Bank 2)

....I have no idea what these two things mean...One guy told me its my O2 sensors....which it very well could be as i hear thats a common problem on mazdas and another guy told me its my catalytic converters...but i thought you only had one of those!? I'm so very confused!! Someone PLEASE HELP!!! Thanks!

 

Actually you have 3 catalytic converters and 4 oxygen sensors 00GrnMillyS. You have a main catalytic converter about midway down the exhaust pipe and you have what are called front warm-up catalytic converters that are built right into each exhaust manifold. The warm up converters in the exhaust manifolds are the ones that are monitored by your engine computer for deterioration and can set codes and turn on the CEL. The main converter is not monitored at all. It could be completely blown out the tailpipe and no CEL or codes stored.
The 4 oxygen sensors are divided into two separate and distinct groups. Upstream or front sensors are used by the engine computer to check and correct how rich or lean the engine is running. There is one of these in the upper portion of each exhaust manifold. Downstream or rear sensors are located just after the warm-up catalyst and are only used by the engine computer to monitor how well both of converters are operating. There are some updated Downstream oxygen sensors available from Mazda that are less sensitive. See link to TSB below. These new sensor tended to work on relatively low mileage vehicles when they were new but if you are getting up there in mileage they will probably not do you any good and new converters will probably be needed. Don't forget that Federal Emissions warranty is 8 years or 80,000 miles and will cover free replacement of these two converters if you are still within both of those ranges.

http://www.mstore2000.com/PDF_Files/01-01-003-944.pdf

 

baby hueyWoW...that was somewhat over my head, but your response really helped out my dad. I do have a few more questions that I'm sure you'll be able to answer with no problem. From your experience how much do you think getting these two converters fixed would cost me? And, considering I've heard that this won't be a cheap fix how necessary do you think it is that i get it repaired? What will it effect and how badly if i opt not to get the repair...And finally, is there anywhere that i could buy these parts cheaper, perhaps online? Please respond! You're helping me out so much! Thanks for your last reply as well!

 

Well, the labor to replace both of the manifold/converters will be around 4-5 hours. Check with a few repair shops and see what the labor rate is for that type of repair to determine cost. Labor rates can range from $60/hour to $180/hour depending upon where you live and type of shop. Was not able to find any aftermarket warm-up converters, only the main converter. OE retail from a dealer will be $416.65 for the right side converter and $754.86 for the left side. Looks like could knock around $250 off that price by buying from www.onlinemazdaparts.com. Use the box labled search by factory part number and use these part numbers. Right cat is a KJ02-20-55XA and Left cat is KJ02-20-50XB. Those are zeros in the part number and not the letter 'o'. You will of course need a few gaskets here and there but those are peanuts in comparison.
If you do not decide to fix it right now what will happen? Nothing really other than the CEL being on all the time. I suppose if they started to really deteriorate and start coming apart or breaking down they could cause a restriction in the exhaust which would give you a loss of power feeling or bogging down on acceleration.
The only thing that could really force you to replace them is if you are required to take your vehicle in for an annual or semiannual state inspection to renew your vehicle registration. They would usually then hook up a scan tool to your car and make sure that you do not have any emission codes stored and that all of your rediness tests have been completed. The rediness test completion is the part that prevents you from simply disconnecting the battery and clearing all codes before taking in for the inspection so your CEL is off when you get there. [sm=bustedsign.gif]
A rediness test is, simply put, when your engine computer does a self test of various emission related systems to make sure they are operating to specification.
Hope the explanation helps both you and your dad but if any questions or doubt then let me know. Will try to explain better.

 

i have recently gone thru this. since we have 2 99's, i also have a scanner that will read/erase codes. you can get one for around a hundred bucks. read your codes, then erase them. make a note on what the codes were, and the date. in our case, we kept having 0421. i would erase it, and at first, it would not come back for several months. as the cats/sensors die, they die slowly. after about 3 years, i would erase the code, and it would be back in a week. so, i changed out the rear pre and post cat sensors, but the code came right back. that means it is the pre cat. i got the rear precat and gaskets, and changed it out myself. took about 3 hours, but i have access to a lift and air tools. looking back, i would NEVER try to change out the precat unless i have a lift. it can be done on jackstands, but it will be a real bear. after the new precat was installed, i could tell the car ran much better, and there has been a slight increase in fuel economy.