Originally posted by rams78110
My car's check engine lights is popping on and off, more off than on. It'll be on for a day or two and then I wont see it for another 5-6 days. 2002 Blazer.
Gunna take it in to run diagnostics on it when I get a chance. Thing is Im short on time to take it in. What do you guys think it could be?Check Engine Lights can be a major PITA. Contrary to popular belief, mechanics don't just "plug in a computer" to find out what is causing the check engine light to set off. One issue could set off multiple codes in multiple systems. What the scanner does is give you a vague idea of where to start diagnosing. A Check Engine light can be caused by anything from a loose/faulty gas cap (seriously check your gas cap) to a faulty sensor/wiring. That is why you will want to make note of anything related to that check engine light. Give your mechanic as much information as possible about the light. Independent Garages in my area charge an average of 85 dollars an hour, if your car has a particularly stubborn, or maybe an intermittent issue it could be tricky to diagnose. The more information that they have to go on the easier it will be to diagnose.
That being said make sure to make note of a couple of key things:
Under what conditions does your check engine light pop on? Note the RPM and whether the engine was hot or cold, whether it came on during city or highway driving.
Does your vehicle have any performance problems? Does it seem like it has lost some power? Is the car surgering? Does it idle rough? Do your RPM's fluctuate at a stop? Does it have a laggy throttle response? Is it misfiring? Do you have problems starting your car? Make sure to take note of anything of that nature. Pay close attention to how the engine behaves, that will also give the mechanic a good idea of what might be going on.
One thing that you can do is take the car to Autozone or O'Reily's and ask to use an "OBD2" scanner. There is a little port on the drivers side of the car poking up from underneath the dash. Turn off your car and plug it in, then turn on your electronics, do not turn your car on. The device will read the trouble codes from ECU on board your vehicle. I will have to put out a disclaimer though, I said this before I'll say it again --- these codes are not necessarily what is going wrong with your car. It could say something about an o2 sensors voltage being low, but in reality the o2 sensor may be perfectly fine, and something else in the system may be causing the o2 sensor to have low voltage. There is always the chance that the OBD2 scanner will tell you exactly what is needed to fix your car. These scanners will work even if your check engine light is off.
I can't stress this enough, CHECK YOUR GAS CAP!!!!!! That is one of the main culprits for check engine lights. If it is bad a new one will cost you hardly anything at all, if its loose all you need to do is screw it tight. Make sure to check the condition of the gaskets on your gas cap.
Let me leave you with one last tidbit of advice: Your check engine light does not mean your vehicle is about to explode. You can ignore that light for a little while. If you're stretched for time you can ignore it for now. The check engine light mostly monitors emission control systems. You would mostly likely be safe ignoring it for an entire month. If the problem is intermittent they may not even be able to diagnose it properly, especially if you're not having any performance issues.
If I were you I would start by checking gas cap, and checking your oil (when did you last change it? GM vehicles usually put up a check engine light if you haven't changed your oil in a long time), you can also check your spark plugs. If your spark plugs are crusty white, or are oily, and smell of oil then you have a problem that needs to be fixed ASAP. These are three simple things that can give you an idea of what is going on inside your engine.
Here is a good article about reading sparkplugs:
http://www.wikihow.com/Read-a-Spark-Plug 
