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Emissions Tests and Check Engine Light

So the check engine light on my 2005 Chevrolet Classic (Malibu) has been on for a while. I really didn’t care until now I’m close to my emissions test deadline. The only other issue with the car is that when I try to put more than 4 gallons of gas in the car, I have to pump the gas pedal a few times to start it after ignition. I have about 150,000 miles on the car. I commute about 80 miles round-trip to work everyday,and not in a position to just get rid of the car and get a new one.

So the Auto Zone guy gave me the codes: P0130 and P0496. He also cleared the light. It came back on after about 60 miles. I would like to know:

1. If I need to get this fixed, any idea what this is and how much its gonna cost me reasonably?

2. Ok, this is bad, but if I can get the light cleared again, and take it over for the emissions test immediately, will it pass or can the test facilities get past the “clear?” I’m in Northern Virginia.

Resetting the light and getting to inspection before it comes back on won’t work. You will then fail because the computer hasn’t finished running all of its tests. There is no way to trick it.

The P0130 refers to an issue regarding one of your O2 sensors. The normal thing to do is check the wiring/harness for the sensor, check for exhaust leaks, and vacuum leaks. If none of that indicates any problem then you probably just need a new sensor. Nine out of 10 shops would just throw a new sensor in there without checking anything.

The P0496 is probably related to your trouble starting the car after getting gas. It is for the evaporative emissions system and has to do with a problem with the purge flow (when the gas fumes are sent to the engine to burn). It basically means that evap flow is detected when its not supposed to be. I hate to tell you but those codes often turn into fishing expeditions. You need a really good diagnostician. If you’re lucky you just need a new purge valve.

I’d actually like to hear from you top 250 and 20 contributers on the entire subject of diagnostic codes. As we all know, often they are extremely general (my favorite: misfire in cylinder x) but even when they do point to a specific system the parts list is extensive.
I know the issue of diagnostic code information sharing is the subject of several lawsuits pitting anti-trust arguments against patent protection.
In your opinion, are car dealers better equipped in diagnosing these problems, or are there specialists out there that do a better job? The reason I ask is that, I agree with you that this can turn into one long part-changing fishing expedition. It seems to me that the dealers should have more experience at least, but also that they may get better information from the diagnostics than would AutoZone or a local mechanic.

There is nothing to share about diagnostic codes. Since 1996, fault code numbers and definitions have been standardized–a P0401 means insufficient EGR flow for every make, model, and engine across the board. That’s federally mandated.

The lawsuits and pending legislation in many states (“Right to Repair”) are frivolous and in my opinion stupid. With very few exceptions, everything your corner garage needs to fix your car is available to them. Hardware, software, diagnostic and testing equipment is all available to anyone who wants to buy. But people want these things for free.

AutoZone, etc. don’t do diagnostics. They read fault codes and give a list of possible faulty parts. There may be half a dozen things causing a given code, but all those parts are easily tested and verified as good or bad if you have the correct equipment and service information.

When the job is finding out what caused a light that refers to a certain code to come on it is very much related to the experiences of the mechanic whether the results obtained are valid. You can ask yourself who knows your car best and it will take a bit of work on your part to figure this one out. At the very least you want the car dispatched to a man that specializes in drivability, not a general mechanic. Along with experience you want the man you chose to be better than average when it comes to intelligence.

[i] the check engine light on my 2005 Chevrolet Classic (Malibu) has been on for a while. I really didn't care until now I'm close to my emissions test deadline.[/i] 

 You should care.  Not just because you may be adding unnecessarily to the pollution of the air you and the rest of us breath, but because you will never know when the car may have another message for you and that next message could be a warning that your car needs attention and without attention an important part may be about to fail.

The thing is that the codes aren’t that general. They always refer to something very specific. Its just that most people assume the specific thing is parts. Meanwhile the very specific thing is some reading from a circuit. The engine’s computer can’t “see” parts - all it can do is send and receive electrical signals. Really getting it is a matter of knowing exactly how a particular system under question works so that you can take into account all of the things that might generate a particular code - and even the conditions under which the code is generated.

Factory service manuals have complete info about this kind of thing - they specify the conditions under which a code is set (the actual conditions as programmed into the computer logic, as in “if this, and that, but not this…”). Then they include complete trouble shooting steps to pinpoint the actual issue. I’ll be the most common first step is inspection of wiring and harnesses & voltage/continuity checks.

Many people, including those in the auto industry, don’t understand the codes and do misinterpret their meaning. As such, throwing parts is probably the most common approach to codes. Its just that its the basic approach for those who don’t really understand what is going on. However, I will say that there can be instances where the diagnostic procedures, while correct, may be so time consuming that an educated guess could be smarter than paying for the diagnostic time.

I would have the light reset again, try disconnecting the battery for 30 seconds, many cars will reset this way, drive it 20 miles or so to hopefully allow the car to be tested and try for an emissions test…There might be a window of opportunity before the light comes back on.

Your car has either 2 or 4 oxygen sensors and sometimes you can change them yourself, saving a considerable amount of money. Properly functioning sensors can improve the performance of your car and might be a worthwhile investment. The EVAP system problem can turn into a high-dollar fishing expedition so I would try and bypass that issue…

If you are not in a position to get rid of a car and get another one, then you need to change your mentality about ignoring Check Engine Lights.

Your car is going to fail its emissions test, unless you resolve the issues it currently has. No amount of resetting the light, and driving straight to the test place will fix this.


  1. You need to get this fixed. Until the actual cause of the codes are diagnosed, it’s impossible to suggest a price. It could easily be $500 or more with the diagnosis. Figure a purge valve or purge valve solenoid, and perhaps an oxygen sensor. And the diagnosios and repair time.

  2. the test facilities won’t discover the problems unless the light comes back on. They cannot read what existed before it was cleared. You’re playing the odds.

Get it fixed. Or at least get it diagnosed and get an estimate. If something destructive begins and you’re not aware of it because you’ve left the light glowing, you’ll regret the decision.

I had a recent code pop up on our voyager, lean on bank 2 or something if I recall correctly. Tried all the suggestions here, clean maf sensor etc. On the net was a TSB about a valve cover that should be replaced with a new valve cover because of a design change. I wasn’t about to do that without verification so off to ford we go. They replaced a plenum gasket and a couple of other things. I asked about my ability to troubleshoot that problem and was told that their machines read more codes and info than the generic ones at the parts store. Do I believe them, I guess I have to as the cel problem was solved.

Thanks for the advice everyone! Got a friend’s husband (a mechanic at a Chevy dealership) to run the diagnosis and change the purge valve for a fraction of what I was afraid it was going to cost. Passed emissions. And love the fact I can fill the gas tank all the way up!

“And love the fact I can fill the gas tank all the way up!”

This could be the source of your problem. If you fill it “all the way up”, you can damage the purge valve. The raw gas getting into the fuel/air stream will fool computer into thinking that it has an O2 sensor fault. Always stop filling when the pump clicks off the first time.

Why did you have your Plymouth or Chrysler fixed at a Ford dealer?