Mechanics

CHECK ENGINE LIGHT(NON-EMMISIONS)

2003 Saturn L300 • 164,500 miles

My check engine light came on, the non emissions related one; it turned on when I got onto the freeway from one exit to the next. When I got home I turned the car, when I turned it back on the light was off. I idled the car for about a minute and the light didn't come back on. What are some reasons that the light would turn on for such a short period of time? And would it be safe to continue driving the car if the light remains off?
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Dsmddn11
April 29, 2013.



What do you mean by "the non emissions related one"? There are well over 1000 potential diagnostic fault codes that can be set but only those that could adversely affect emissions are required to turn the yellow Check Engine light on.

You can get an idea of the severity of the problem that was detected by how the light acts. For problems that can not affect emissions, problem with an air conditioning compressor relay, for example, will set a code but will not turn the light on. If the problem could result in increased emissions the light will turn on, but if it's relatively minor, the light will turn off while you're driving if the problem goes away.

If the problem is a little more serious the light will turn on when the problem occurs, then if it's an intermittent problem and it goes away, the light will stay "latched" on until you stop and restart the engine. At that point the light will stay off until the problem occurs again, then it will stay on until you restart the engine again.

Still more serious problems latch the light on all the time the ignition switch is on, even if it's intermittent and stops acting up. Even if you find and correct the cause of the problem, the light will always be on until the fault code is erased.

The most serious problems are when the light is flashing. That means stop the engine right away. Too much raw fuel is going into the exhaust system and is going to overheat the catalytic converter. That will melt the catalyst into a glob causing it to become plugged. That's a very expensive repair that often has an inexpensive cause.

You can go here to get an idea of what can turn the light on:

http://www.2carpros.com/trouble_codes/obd2/P0100

It's important too to understand that even when the Check Engine light turns off, the diagnostic fault code will still be in memory. Chrysler products are very good about that. When the light turns on there WILL be a code to tell you what's going on. GM gets a little more frustrating because they also use "pending" codes. That means the computer is watching something closely to see if it needs to set a code. If you don't read the codes right away before the light goes off you won't know what was wrong.

Regular codes stay in memory even though the light turns off. That is a common source of misinformation at a lot of auto parts stores that read codes for you for free. A lot of the guys think there are no codes to read if the light is not on at that time. That is not correct. What can happen is if an intermittent problem does not occur again, the code will usually erase automatically after a period of time. For Chryslers that is 50 engine starts which is typically about two weeks. That gives you plenty of time to read them. Chrysler codes can be read right in the car with no special equipment needed. You used to be able to do that on GMs before the '96 models but it was a little more involved. For '96 and newer you need a code reader or scanner.

You can drive the car as long as the light is not flashing but emissions may be up and fuel mileage may be down. It is also important to understand that fault codes never say to replace parts and they never say a part is bad. About 50 percent of the time a sensor referenced in the code is defective, and the auto parts store guys will want to sell you that part, but half of the time there is some other cause. Fault codes only indicate the circuit or system that needs further diagnosis. There could be a broken wire, corroded splice, stretched or corroded terminal in an electrical connector, or a wire rubbed through and touching a metal part of the car. About half of the potential codes don't even mention a sensor; they only tell you of a condition such as "running lean too long".

Caradiodoc
Apr 29, 2013.
The non- emissions light is the one with the wrench. The car has two "SES" lights, one for emissions related problems and one for non emissions faults. One has a car outline with a wrench inside, the other is the standard engine outline.

So basically since the light is off, I have to wait for it to come back on to find out what the fault is?

Tiny
Dsmddn11
Apr 29, 2013.
Nope. That's what a lot of auto parts store guys think. If a code was set it will be in memory even when the light is off. If it was a pending code, that requires the light to be on to read it if it didn't stay in memory.

Caradiodoc
Apr 29, 2013.
Ok, I'll get the code checked out. But the car should be safe to drive though right?

Tiny
Dsmddn11
Apr 29, 2013.
You can drive the car as long as the light is not flashing but emissions may be up and fuel mileage may be down. It is also important to understand that fault codes never say to replace parts and they never say a part is bad. About 50 percent of the time a sensor referenced in the code is defective, and the auto parts store guys will want to sell you that part, but half of the time there is some other cause. Fault codes only indicate the circuit or system that needs further diagnosis. There could be a broken wire, corroded splice, stretched or corroded terminal in an electrical connector, or a wire rubbed through and touching a metal part of the car. About half of the potential codes don't even mention a sensor; they only tell you of a condition such as "running lean too long".

Caradiodoc
Apr 29, 2013.