Daughter's Millenia 2000 2.3 S purchased 9/06 with 100K miles from dealership (one owner) with all receipts with CEL on with codes P0421, PO431 (CAT codes) only. HAve been driving it this way since ....113K miles now.

Ran fine with decent fuel economy (15 to 16 mpg) and periodic checks showed the same two codes. Daughter drove 4 hours home no problems still had CEL on. After a short drive next night it would restart and idle roughly but not rev when accelerator pressed, then die. It would crank and only idle roughly (not rev) before stalling out. After leaving it over night it started right up, good idle, a little sluggish, I drove 10 miles checked codes, the same P0421, P0431.

Added "heet" gas line anti freeze to a new tank full of premium. Drove another 8 miles turned off for 5 minutes to have same problem. Waited 30 minutes, it started and was able to drive 3 or 4 miles before stalling. Finally had it towed to a Chevy dealer(I know bad move but was trying to get daughter back to college on a Saturday-only dealer open). They finally were able to repeat same condition and saw same two cat codes, but did not think the problem was related directly to Cats, suggested I take it to a MAzda dealer. Car required a jump at Chevy dealer when I picked it up, but no codes at all (Dealer had erased them), drove 8 miles home and car ran great.



Next morning no power, I put it on the 20 amp battery charger for four hours. Started and ran good for 7 or 8 miles (no codes) let it idle in drive way after five minutes it stalled, but still no codes. Tried next morning battery dead, no interior lights or electrical drains on. Car with battery charged will not stay running now, still no codes.

1. Before I tow it to the Mazda dealer.......any suggestions other than the CAT?
2. Is there a special aftermarket CAT delete kit with special sensors?
3. How difficult is the replacement if it is indeed the CAT / O2 sensor?

Sorry for length but want to be thorough.
History;the Original owner had Mazda Dealer paperwork showing a CAT (KJ02-20-55XA), gasket converter (KL19-40-450) replaced under warranty at 47K with a F0201BRX service code of Exhaust manifold R & R right side. At 50K miles the O2 sensor (KJYI-18-861) was replaced under service code F0811ARX O2 sensor, R & R, one or two. At 84k R & R, timing belt, tensioner, waterpump, sepentine belts, tune up, air filter, and fuel filter.

 

Sounds like the dealer killed the battery. I would load test it to be sure. Most any parts store will charge/check them free. As far as the running problems i would clean the MAF hotwire first,check for vacuum leaks,check the ECT,and fuel pressure. Could be simply a battery with an internal plate cracked/shorted. I have seen batteries do strange things to cars even when they start the car fine.

 

sounds like a fuel problem. first off, the cat codes might not be related. there are no codes for like a clogged fuel filter(mazda recommends every 60k). if that has never been changed, i would start there. when you remove the filter, dump out whatever fuel is in there into a glass jar, and look at it. it should be clear. if not, you may have debris/bad fuel in the tank. i believe we went thru this; right after a fill up, we got flashing ce, and missfire codes. i threw in a couple bottles of heet, and it cleared up, but codes came back. in our case, it was always missfire(0300) and cyl specific(0305). wouldnt you know, it is always the hardest cyl to get at. i ended up changing all 6 coils(cost me like 800+). since you dont have missfire codes, i know this aint your problem, but the bad gas might be. last on the list is fuel pump. i spoke to a guy on this forum in atlanta who had similar symptoms, and he had all kinds of stuff changed at the dealer, finally they put a fuel pressure gauge on it, drove it, and sure enough, the fuel pump was bad. if you can tap into the line back there where the filter is and drive it, that is the best way.
we also(we have 2 99s') have gone thru the 0421/31 syndromes, all 2.3 owners will. everyone will tell you to change out the post cat sensors, there is an sib on it, yada, yada. the ONLY time changing the post cat sensor works is if you erase the code, and it takes time for it to come back. otherwise, it is your precats. there are a couple of aftermarket cat suppliers, catco is one, eastern, and one place that recycles cats, brown recycling. you will be amazed at the performance increase with new cats.
your fuel economy sucks. we get 20-22 consistently, mixed driving. what has happened is because of the ce lite on, the system has gone open loop, and it is running on factory default maps. that means richer, which is not good for precats. also, we have been running mid grade(89) octane for years with no adverse effects. having gone thru vapor lock a lot(not with the mazdas) i am careful to use name brand fuels. google 'top tier fuels' to get a list of approved brands.
i am surprised that when it starts to miss, you dont get a flashing ce lite, or the tcs off/tcs lites come on. if that happens, then the car goes "limp home" mode-dont rev above about 2800.
dunno about where you are, but here in texas, if the car wont pass state inspection(ce lite on) you can make the prior owner take the car back, and get a full refund. if you cannot perform some maintenance on this car, i would strongly advise you to get rid of it. even the dealer has little to no knowledge/experience with this car. dont expect to take it to any shop, and have them repair it. you will be paying for them to learn about your car, they will throw parts at it, and then most of the time, they will give up. it will eat your lunch. both of our cars have about 110k, and i have done the following: cv axles(i GUARANTEE you they will go out-more than once), seat heaters, motor mounts(dont get ebay, and genuine are pricey), precats(BIIIG bucks, lots of labor), p/s pump(ate my lunch, big time), timing/accessory belts, accessory belt tensioners(352 each!!!!), radiators, upper leading and trailing links, sway bar end links, fuel injectors, solenoids, vacuum lines(these will eat your lunch, big time), even the spark plugs/coils are a bitch to get at. one of the bigger problems with this car is the system that watches boost. it is uber **** about overboost, and will throw the car into limp home mode a lot. diagnosis is difficult, and, of course, parts are expensive. i would not put my daughter in one, unless she was living at home. my wife drives one daily, and it has gone thru a lot. i also do a lot of preventative maintenance, every oil change i drain/refill the p/s resevoir. i flush coolant/brakes/transmission fluids yearly. i have full size spares in both cars. if i see a drip on the garage floor, the car stays here, and she drives the other one to work(i am retired). the car has NO resale. but overall, i think it is a very well made car(i sold parts for bmw and mercedes for years, and i think it is of equal quality), and we would like to keep them for a long time.

 

Thanks keninn/hixx for the quick responses.

keninn, it sounds like you and your wife love the Milly's like my daughter does. We've been through a lot of the same problems you shared, many of them were taken care of by the original owner who meticulously maintained this car and kept all the receipts, which gives me some comfort I'm working on the short list. I' m afraid to start all over with a new used car.
We're in Indiana so NO emmissions test to pass for state.
Local Mazda Dealer via phone said replacing both PRE-CAT's would be $2,950 (OEM) P & L and the O2's would be $600-$700 (OEM)in just parts. They have not seen the car in fairness to them, but I'm not ready to sign up for that kind of coin.

I don't have the service manual here at work but will try changing out fuel filter if I have time before I travel next.

Hixx...I will also pull the battery and have load tested, (I'm now on a first name basis with all the Advanced Auto guys from borrowing their scanner).

1. Is the "MAF" hot wire you refer to the Mass Airflow sensor? Could you please clarify?
2. Regarding Vaccuum leaks...is there a particular vaccuum line or spot that is most suseptible to burning , cracking, coming loose, accidently being pulled off? I'm looking for a starting point other people may have had similiar issues with.
3. Forgive me (no manual here) ECT?
4. Have either of you or anyone else ever replaced the precat's on your own?

Thanks again....I feel there is some hope for a less expensive, solid fix.........for now anyway.

 

if the maf was bad, you would get a code.
if your vacuum system is bad, you will get codes. most common, 0170/73
if you need a manual, go to the other mazda forum, mazdaworld.org. after registering, look for millyowner, he has a link to a 96 fsm. very little difference. he also has links to wiring diagrams and vacuum routings. i have all the manuals, wiring diagrams, etc, but they are for 99my specific.
i have replaced both precats. KJ02-20-50XB, left(front) bank, mazda sugg list price, 1016.81, tasca mazda discount price, 701.45. KJ02-20-55XA, right(rear) bank-561.25/387.18. you will also need gaskets, a lot. to get the right bank off/on, i pull the exhaust. the entire thing, you will see. i also use a lift. the left bank, i pull the radiator, which is a job in itself. but then you only need to pull the "Y" pipe. i would NEVER do either without a lift.
the codes you are getting have NOTHING to do with the oxygen sensors before the cats. and if you want to replace them, just get generic, and splice them in. mazda does have some sensors that were supposed to cure the 0421/31 codes, but generic works just fine.

 

If the MAF is bad it will throw a code but a little dirt on the hotwire in it wont always throw a code and if it does it wont be an MAF code. More like lean both banks or something. Common as dirt in any event. It only takes 2 minutes to clean and is part of a tuneup in my world.

 

lean both banks is p0170/0173, and is always vacuum leak. 99.999% at the tee's. pulling the mas is a bit more involved than 2 minutes. if you go to a generic place to pull codes like autozone, and you get the 0170/73 codes, they will tell you most likely the mas(p0100). they read from a book. dunno where they get info from. but it's wrong. again, diagnosis is critical for the 2.3. if you do seaches on any forum that has the 2.3, you will see lots of posts on certain codes/problems. 0421/31 are very common, 0170/73, 0300-06, and now becoming very popular, 1525/26 with 1540. all i am saying here is to be careful WHERE and WHO you let repair your car. they probably know less than you do about the car.

 

2/21/2009- I pulled the battery and had it fully charged and then load tested at Autozone. It tested fine. I thouroughly cleaned posts and cables and it is staying charged.

Replaced the fuel filter. Hard to tell if the fuel coming out was really dirty rusty or if it was from surrounding clamps, etc. The fuel didn't smell quite like regular fresh gasoline to me when i dumped it in a jar. Fired the car up seemed to run good drove 30 plus miles a couple of times no CE light, no performance problems. Daughter came home from college Thursday to pick it up, drove 40 miles around town and both CAT codes (PO421, PO431)came back but with no noticable engine performance issues when the CE came on. I've since bought a couple of OBDII code readers giving her one to keep with her car. I drove with her this morning car seems to run fine so I erased the codes.

She left for school (with a friend following her back) and the car lost power after 75 miles. She did not notice if the CE light was on or not as she was concentrating on pulling over. Car has same symptoms as before original problem........will idle rough put push accelerator to floor and it stalls. When she read the OBD it pulled a PO725 code "Engine speed input circuit"?

Tha manual I have on the 99 Millenia doesn't even list that as a code I' checking the OBD CD for more info.

Any ideas?

 

0725 is engine speed input circuit malfunction. i believe this is usually in conjunction with 0335, which is crank position sensor. i seem to remember seeing a few posts with this code being thrown from a vacuum problem, too. try doing a search on mazdaworld.org.

 

2/21/2009- PM Went to pick up the car after daughter left it on side of road for 4 hours. Erased the code, car started right up. Drove 50 miles toward home until car died........complete loss of power with No CEL. SCanned for codes .....none. Car will not start after waiting an hour.

2/21/2009-REturned after 2 hours car fired up, no CEL.

Drove home the remaining 10 miles CEL came on after 8 miles codes for CAT are back (P0421, P0431) engine performance okay.

Could the bad cats really be causing all this grief?

I have a scanner and can capture live readings of the O2's, etc. would this help diagnose if the sensors are bad? what's a good/bad reading?