OBD/Smog Check Frustration - Mazda Protege LX
September 9, 2010 3:09 PM   Subscribe

Why won't my car's OBD system re-set and clear the CA Smog Test?!

Took my car (1999 Mazda Protege LX) to the mechanic back in June after the "check engine light" kept coming on. Original estimate was for a new catalytic converter, but he diagnosed it as an oxygen sensor issue, replaced it and also reset the OBD system.

Two months later (and two weeks before my car registration & smog check are due), my car failed the smog check. I've taken it back to the mechanic and also got a second opinion from another mechanic. To date the advice I've received was to drive it under certain conditions in order to reset the drive cycle:

* 5 minutes on idle after starting cold w/aircon etc shut off

* 3 minutes at 50mph

* 1 minute at 40-60 mph.

I've taken two 100+ mile drives and it's still failing the smog check. I've been told that it's a system issue, not something where I can have a component replaced. The registration is due in two weeks so I'm about ready to pull out my hair, or worse take it to the dealership. Any advice/experience or a direct line to the Car Talk guys would be much appreciated.
posted by gov_moonbeam to Travel & Transportation (6 answers total)
I have the same car except it's the ES model. I also had the same problem, check engine light came on intermittently sometimes stayed on for a long time, sometimes would turn off for a couple of days at a time. I also had the run around with multiple different solutions which would get it to turn off for a little while, but it would inevitably come back.

The end solution.... replacing the catalytic converter... unfortunately. The only good news is after doing that the light has stayed off for the last 9 months.
posted by Beautiful Downtown Burbank at 3:33 PM on September 9, 2010

It might sound kind of obvious to put it like this, but the drive cycle isn't completing because there's a condition that's not being met. Obviously, that condition isn't the type or duration of driving that you're doing. What's more likely is that some value that the computer is looking for as a trigger to initiate one test or another is never the right value.

Many competent mechanics can look at the fault codes and look at stuff like Readiness Monitors and make very competent evaluations based on that information. The kind of mechanic that you're looking for is the Uber-competent type that knows how to look at and interpret the Mode $06 data that the car's computer stores.

About Mode $06:
So, by now, you're familiar with Readiness Monitors. Basically, each individual emissions system has an overarching self-test that needs to be complete and "passed" at the time of the emissions test. Now, each Monitor is comprised of a number of more detailed tests. Mode $06 shows the results and parameters of each test. Often, it's in hexadecimal gibberish and you have to use a table buried deep in some repair manual to decipher it. By observing each Mode $06 test, a good technician can see which tests aren't being run and the inputs or sensors specific to that test. It'll help them narrow it down. It could wind up being something as simple as a temperature sensor, while always being in spec, never shows a hot enough engine temperature to initiate certain tests. Be warned, however: many mechanics will not know what you're talking about if you mention Mode $06. Check iATN.net for really top notch shops in your area.

Additionally, check with Mazda. There might be a recall or a fix that corrects for the error in setting Readiness.
posted by Jon-o at 3:51 PM on September 9, 2010 [2 favorites]

Check in at the Mazdas247.com forum... It's a wealth of knowledge on anything and everything Mazda. Pretty sure the guys on the Protege forum would be able to assist you with this problem... You might even have luck finding someone local to give you a hand.
posted by ganzhimself at 4:33 PM on September 9, 2010

Your description of how to reset the code left out the part where you disconnect the battery for ten minutes.
Do that first.
Then do the driving things you described, to see if the check engine light comes on again.

It would really, really help to know exactly which ODB II code or codes your car was signalling.
It would really, really help to know exactly how your car failed its smog test.
Was it hydrocarbons? Nitrogen oxides? At 15 mph? 25 mph?

Without specific codes, we are left to guess if it is specifically an oxygen sensor failure, a air pump problem (which provides extra air to the catalytic converter when the engine is running rich), or an idle air bypass problem (or its equivalent).

Resetting the ODB "saved codes" with a simple and cheap ODB-II scanner is the most reliable way to reset your codes. Fifty bucks can buy you that scanner/resetter from a number of manufacturers (I can't help you with those modern devices and protocols. I'm all EEC-IV and ALDL).
posted by the Real Dan at 10:02 PM on September 9, 2010

When I had a similar problem with my vehicle, I was told to contact Ford to find out the specific drive cycle requirements. Have you contacted Mazda?

I'm not sure about California, but in Arizona if you take it for the initial test before your registration expires and it doesn't pass, you're given a 30-day grace period to get the problem corrected and the vehicle retested. It relieved some of the stress for me.
posted by curie at 4:48 PM on September 10, 2010

Response by poster: Geez, 4 different mechanics and $180 later, finally found out the problem. When I had the work done back in June, that mechanic replaced the battery cable. Removing the cable essentially wiped out all the memory and thanks to that particular make/year, getting it to reset is super flaky. I actually went to the DMV today to plead my case & got the paperwork to have it be a FAIL so I could get a ($50) 2 month extension for the check. Went back to the original smog guy to get the fail and he actually checked the engine + the requirements for that year, so I finally passed.

What a PITA! And for anybody who's reading this in the archives:

Late 90s model for Mazda & Nissan have this problem
If you replace the battery cable, it can wipe out the codes for your OBD.
posted by gov_moonbeam at 11:34 PM on September 15, 2010

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