Question for you auto mechanic types

[SteveA]

Tomorrow morning I'm going to look at a 2000 Mazda Protege I found on Craig's List, for my son. So far everthing sounds good on paper. BUT. The Carfax report shows the car failed emissions tests in 2006 and 2007. Within a month of each test another was taken and the car passed, both times. Let's say this car checks out mechanically to my untrained eye, could these emission failures be a cause for serious concern? In other words, if worst case were an oxygen sensor, I can live with that. I can't live with an engine rebuild. Any help is appreciated.

[AAlmeter]

Well, the decent thing is that emissions failures give you a full year to fix the problem. I would most certainly bring it up during negotiations if you decide to buy.

There are some basic causes that bring up the codes, air fuel or ignition systems (you would notice these upon driving), vacuum leak (easy fix, sometimes tough to find), EGR, EVAP, and PCV systems (not bad fixes, and really only effect the inspection...in most cases), and the exhaust/emission system (can get costly...especially with legal O2 sensors and the cat and determining which is malfunctioning).

As far as the failed tests and then the retests, a car that fails its OBD inspection (the computer emissions test) will have to be reset. After it is reset, the sensors will "zero out" and read nothing. At this time, in most states, it will not pass inspection. However, these sensors will not come "online" at the same time. If the car can be hooked up to the computer while enough sensors are functioning to meet the state quota and before the offending sensor signals the computer to send a fault message, it will pass.

*Please keep in mind that I've only done NYS inspections. It may vary, especially in tight states like CA

My advice would be to ask for a long test drive....and if anything pops up (the check engine light will turn on) to take it to a place like autozone where then can plug in to your OBD II to give you your fault. From there, feel free to post here, email me, google it, or ask the autozone dude and you will get a fair idea of any repairs you may need....if any. If nothing pops up, you may want to take it to a full service shop, and they will be able to tell you if all sensors are functioning (meaning it has not recently been reset...something done either via an OBD II scanner or even disconnecting the battery).

Most of your serious emissions issues will result in drivability issues (missing cylinder...rough idle), the ones to be wary of are costly problems such as a cat or hard to trace O2 sensor problems. Many of these problems, once identified, can be easily fixed with a little home monkey wrenching.

I'd also familiarize yourself with some internet forums that can lead you to possible causes for, and solutions to, any problems you may find.

As always, its a crap shoot with a used car. Good luck.

[SteveA]

AAImeter - Wow! Great, extensive answer. Thanks much for taking the time to share your knowledge.