Model: 626-LX Sedan
Engine: 4 Cylinder
Liter: 2.0 liter engine
Emission: Calif. Emission
Current Mileage: 124,450
I’ve read many columns of questions and answers of your website and spent a great deal of time reading and learning, but did not see this question and answer (the problem I’m describing below) on your website. HELP.
Late Nov 2006, my car passed Safety (although emission did not). The auto shop kept coming up with a trouble code P0421 (this code causes orange malfunction check engine light to stay on dashboard), orange light looks like a battery symbol.
Shop informed me H02 Exhaust Oxygen Sensor may be the problem, they checked the old 02 exhaust oxygen sensor, showed me the part that looked worn and in bad condition. After some thinking, I agreed to have shop replace it ($227.25 for the part) tax, etc. = $268.89.
After the new 02 exhaust sensor was replaced. The shop told me to drive it (40 – 50 miles); believe P0421 should go off. Having driven to & from work of 96 miles in 3 days, took car back to shop, code P0421 came up once more, they asked me to drive it some more. I drove the car for few more days (to see if orange malfunction emission light may go off dashboard). It didn't.
Shop thought may be the H02 heat sensor may also be worn, checked the part, showed me the old part (most likely original part of the car that is 10 yrs old). I asked if I were to replace H02 heat sensor, would orange malfunction light stay off; they said it might although can't say for certain but worth a try. Based on my instinct and gut feelings, I thought they were honest of their opinions and gave me their findings (to let me decide to replace the 02 heat sensor or not).
They referred to their auto booklet which indicates the code P0421; showed me the page that it is “02 sensor problem”.
H02 heat sensor (was later installed, cost $200, add on tax, etc. = $240.00). Afterinstallation, orange malfunction light still came on (dashboard) when starting engine; shop's digital reader still came up P0421 code. Since they’re reset the computer, shop suggested I drive it some miles; orange malfunction light should go off.
Few days later, it seems that no matter how many times I've driven the car and put on mileage, orange malfunction light stayed on dashboard.
When this light stayed on, it does NOT effect the car, performance or whatsoever. It also does not cause any bad or poor air pollution that I noticed; I also did not detect any smoke, smog, or poor air pollution, no bad or unusual smell (even when I am behind the tail pipe). The air appears to runs CLEAN. I am beginning to feel the emission light (may be giving a faulty reading)?
My assumption is (computer inside the engine may be causing a faulty emission light to come on (?) I need help answering this question.
Since the orange light stayed on and no matter how many times the shop reset computer; the shop now thinks may be it is (UPPER GASKET OR UPPER MANIFOLD, may be the culprit). The upper Gasket while other shops call it "Upper Manifold") is located front of engine.
Shops such as MIDAS, MASTER MUFFLER, including the shop that replaced my (H02 Exhaust & H02 heat sensors) thinks the problem of P0421 remain on dashboard may be the (upper manifold) problem.
1. Since I didn’t detect any bad air pollution and my car is running in exceptional condition and very reliable; never breaks down. Easy to start in cold weather, reliable start in hot weather, excellent mileage. Based on the problem described, how do I know whether it is the (Upper Manifold) that is the problem? Or if the (CATALYTIC CONVERTER) that may be the problem?
Auto repairs are $$$, I need to rethink carefully before spending hard earnings. I don’t want the shop to tell me it is the (upper manifold) that needs replacement. They may be wrong (and later tells me it is the catalytic converter) that needs to be done.
Upper manifold from Master Muffler's for my car is quoted: $510 (part & labor), rear converter (which is the back one that is underneath the engine $180). I phoned another Master Muffler shop, they quoted me $650 upper manifold; rear converter $200.
MIDAS quoted me $865 (part) and $80 labor. Interestingly, when I called yet another MIDAS shop, quoted me a$320 (part & labor).
I called Mazda Dealer to check on (upper manifold) $330 and $80 labor. The parts dept educated me that very seldom, their shop has to replace rear converter, most commonly & almost all of the time, it is the (UPPER MANIFOLD) that costumers bring in their car for repairs of this problem. Rear converter is $1,156.
Please see if you can help answer my questions and provide me with some guidance, it would greatly help me sort out my budget and help me understand what I am dealing with. Thanks.
have the same problem?
Wednesday, December 13th, 2006 AT 1:02 PM