Check engine light just came on in 2000 Mazda protege, how do I perform a diagnostic test to show the code?

Question

I have had no problems with the car and there are no symptoms

Answer 1

You can have the code pulled - often for free - at some auto parts stores. Pulling the code though is just that - finding out what the code is. That is not the same thing as a diagnostic, which is finding out what caused the code and the code is just the symptom detected. It does not, in most cases tell you what is actually wrong in and of itself. Frequently that requires more information than a simple code reader will tell you, which is where the "diagnostic" part comes in and why mechanics who do diagnostic make the big bucks.

Still, sometimes a quickie code reading can be useful. Just don't fall into the trap of "you have an oxygen sensor code so the sensor is bad" or " you have an EGR code so the EGR Valve is bad." Usually that's not the case.

I suppose it helps to explain what is involved.

Let's start with the basics. The Powertrain Control Module in your vehicle is a computer that both runs and monitors all the functions in your engine For emissions compliance purposes when the PCM finds a problem with some facet of the engines operation that might effect emissions it triggers a fault code relating to the nature of the problem detected. When this fault code is registered and stored in the PCM the check engine light is illuminated. If it is a Type 1 or "hard" code, the light remains illuminated until the code is manually removed by using a scan tool or code reader designed for that purpose which plugs into the PCM. This same tool allows you to read what the code is.

Let's use an example of a very common code; A misfiring cylinder would trigger a P0300 Random Cylinder Misfire code, which you would then see on the tools display. Possibly, this same problem might trigger other codes too. Let's throw in a P0301 - Misfire in Cylinder #1, just for fun.

So you've hooked up a scanner or code reader and found the code(s). Now what do you do with this information? Does just knowing the code tell you what to fix?

Usually not!

The code just tells you where to start looking because what the fault code gives you is the symptom, not the cure.

Example; If I were to post a question here saying I had a P0300 and P0301 code for a misfire I bet I would get a dozen responses saying to replace the spark plugs. However, spark plugs are only 1 of many things that could trigger this particular code. If there is an individual ignition coil for each cylinder it might be a coil failure. Barring that, it could be a faulty ignition wire or spark plug tube (for coil-on-plug setups). On dual-overhead cam engines oil could be leaking from the valve cover O-ring that seals the spark plug hole in that cylinder. Or the fuel injector for that cylinder could be malfunctioning. But even then is it a bad injector, a clogged injector or a problem in the PCM itself which is causing the injector to not fire when it is supposed to? Perhaps a mouse chewed through the wiring harness for that injector (seen it more than once)? There are other causes too but you get the idea.

So, to find out why your check engine light is on you need to start by having the code pulled. This can be done at an auto parts store - often at no charge - but these guys are not equipped, trained or qualified to do the kind of diagnostics required to properly identify most problems. Even to find a parts guy (or gal) with a remotely useful knowledge of parts is a rare thing indeed. These folks use cheap "Code Readers" that cost just a few hundred dollars and that only read what the code is and don't offer any troubleshooting tips or diagnostic aids. Often the parts store folks will do things like pull a misfire code and sell you some spark plugs that don't fix the problem. Or sell you an EGR valve because they pulled an EGR related code but that won't fix the problem either because a the EGR issue is the symptom, not the problem.

You could buy a code reader for yourself (really cheap ones start at under $100) but I don't recommend it. The amount of information you get out of them is really quite poor and the number of times you will use it rare indeed. How often does your check engine light go on after all? Most cars go through their entire lives without ever having one.

Or you could take it to a mechanic who has a Diagnostic Scanner that costs several thousand (up to $10k for some units) plus hundreds of dollars/year to update which can pull up not just generic codes like the cheaper readers but also vehicle specific codes. It can view everything that is happening in the engine in real time, see a snapshot of exactly what the engine was doing the instant the code was stored, has troubleshooting tips and specs for all of the related sensors, electrical components etc. He's not gonna do this for free. He's gonna want $80-150 for the pleasure but then, your chances of success are much higher. The problem may be a simple one, it may not, but its the expertise and the equipment your paying for. Do whatever you want.

You could even ignore it and put black tape over the light if you so desire. Whatever works.

Answer 2

Modern cars are run by computers which tell the engine how much gas to inject, what the timing of the sparks should be, etc. This all changes based on driving conditions - air temperature, density, exhaust gases, grade of gasoline, how hard you are pressing on the accelerator, etc. To measure these driving conditions and compute the settings, the computer relies on electronic sensors wired into the engine, fuel injection system, and exhaust. If one of these sensors goes bad or if the wiring goes bad, the computer will get faulty readings for the sensor, not be able to make heads or tails of things, and will sometimes go into bad states, signaling the "Check Engine" display and faulty running behavior. So you will mostly likely find that a sensor has gone bad. I once had an '86 car which would cut out at certain temperatures while driving down the freeway. It was due to a faulty sensor wire that failed to have a good electrical connection at certain engine compartment temperatures. It worked at cold temperatures and warm temperatures but not a range of inbetween temperatures. That took a long time to diagnose. On board diagnostics (OBD) are much better now than back then. Good luck.

Answer 3

Mazda Engine Codes

Answer 4

When the check engine light comes on, the first thing you do is pop the hood and check to see if the engine is there.

OK, OK, no too funny but that is almost all you need to do The light is triggered by the computer, mostly for reasons having to do with emissions. Some sensor is reading out of range for the current driving conditions. There isn't any hurry to do anything about it and may times the condition will "go away" and the light will go out.

HOWEVER!!! If the light is blinking, DO NOT DRIVE it. You could be getting raw gas into the converter where it will burn and destroy the converter. That is big bucks.

Another thing, depending on your state, the car may not pass inspection with the light on.

Pete

Answer 5

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My subaru did that once when the gas tank cap wasn't screwed on tight enough to prevent an evaporation sensor from being tripped. It made everything go haywire...cruise control light flashed non-stop and the check engine light came on too. I thought the car was a lemon and it only had 600 miles on it at the time! Took the dealer less than 15 minutes to confirm it was an issue with the gas tank cap not being tightened enough and clear the code. Since then, I've had no troubles.

Answer 6

You need a scanner in order to be able to read the codes. The scanner is a hand-held computer that hook sup to the car, and it also needs to have that specific vehicle information. Your best bet would to be taking it to a place like AutoZone where they will scan the codes for minimal or no cost. The codes will tell you what needs to be fixed if anything. Sometimes the engine light will come on if you recently had to jump start the vehicle or something like that.

Answer 7

Go to Autozone or Advance. Ask them to run an ODBII test on your vehicle. They should do that free of charge. You can get a reader for your own they run about 150-200 dollars

Answer 8

well to perform the test you will need to gt a obd 2 or a code reader to do it if you do it yourself then you wil have to go to a part store or someplace to get one andi can tell you they ae not cheep they start at about 100 and go up depending on what you want it to do or you can brin it to the shop and have them look at it

Answer 9

you can usually go to an autozone and they will scan the computer for free. or if you want you can purchase your own scanner. the lower end models start around $75. chech ebay

Answer 10

You can take it to auto parts stores(some) and they will plug it up and check the code that tells you why it is on and sell you the part to fix it,,,