If my check engine light went off....?

Question

will a diagnostic test say there is a problem with the car? Or is it only when the lite is on?

will i pass an inspection, or will the diagnostic show there may be a problem?

Answer 1

If the light isn't on and the car is performing as it should, don't worry about it. LOTS of things will turn the light on including sometimes a loose gas cap.

Changing the typ of gas you use, may make it come on until the computer adjusts. There are several sensors on the vehicle and any one of them may turn the "check engine" light on. Pops

Answer 2

If the light is not on at the time of the inspection, you should pass. It will communicate a past and pending failure if they are present, but the demands of the emissions test are that the light not be illuminated.
The test facility may advise you that there is a pending or intermittent condition, but as long as the light is out, it should pass on that level. The car may fail for something else, such as emissions or non-functioning devices, but the light will be OK.
If your car is newer than 1996, it must conform to the OBD II protocol. This system also monitors non-computer items (fuel cap, EGR valve, etc) and must be driven a certain way for prescribed period of time for the monitors to be deemed "ready". If the monitors have not run, your car WILL fail the test.
So if you clear the codes, the monitors will clear also, and must be re-set in order for the emissions test equipment to know that there isn't a failure.
For more information concerning the OBD II Drive Cycle, GO HERE--------->

http://www.obd-codes.com/trouble_codes/gm/gm-obd-driving-cycle.php

This page describes a G.M. drive cycle, and is pretty generic in terms of specificity. It can be applied to most cars, in the same order, and as it is prescribed by the Federal government, will allow most monitors to run in the shortest period of time and mileage.
BUT--it is very specific; it must be followed exactly, or some of the monitors will not run.
The drive cycle MUST begin with a COLD engine so that the computer can "see" a rise in temperature of > 60° F, or none of the enabling criteria can be met.
If this is too dificult or confusing, I recommend that you drive the car under NORMAL circumstances and habits for at least 300 miles, to include cold starts, stop and go driving and some freeway driving, and that using the cruise control for 7 - 10 miles a couple of times.

Good Luck

Answer 3

Yes, the light was only to tell you that there was a problem detected by the computer in the vehicle. Its codes are stored in memory, and when you have a chance to get the diagnostic done, it can be pulled up to tell you the code, thus telling you what the problem is. Hope this helps, good luck.

Answer 4

There could still be a problem with your car, even if the lite is off. The check engine light is usally caused by a little valve on your engine that gets plugged, causing reduced milage. If the valve keeps coming on, it may have to be replaced.

Answer 5

if it only flashed on and then went away prob no worry...you can still go to autozone or some such and have them hook up the diagnostic thingie and see if it saved a code.

Answer 6

a diagonstic test will see what the problem is ,is your vehicle runnin rough? could be fuel injector, i just went through it myself
they had to replace wire harness and fuel injector, it ran like crap
my light didn't stay on all the time,it would say check engine.

good luck hope nothin to serious..

Answer 7

Don't worry about those lights. They're for idiots.