why would theOBD-II light come on?

Answer 1

90% of the time and ODB2 light comes on because some emissions sensor has detected a problem.

You can get an initial reading to determine which sensor triggered the ODB2 from a parts store such as Autozone for free.

Sometimes the fix is as easy as replacing the air filter in the car or tightening up the gas cap.

Good luck.

Answer 2

The "Check Engine" light is triggered when the PCM has detected a failure or fault in one of the systems or circuits it monitors.
Vehicles built since 1996 are required by Federal law to illuminate the Malfunction Indicator Lamp (MIL) only when there is a fault or failure that has the potential to cause emissions to rise above acceptable limits, and for nothing else.
If there is a sensor that causes the engine to not run well, the light will come on because the emissions could rise while operating in that condition. A loose fuel cap has nothing to do with the way the car runs, but can certainly cause a rise in the vehicle's emission level.
If your light has come on, I recommend that you take it in for diagnostics and repair. To continue to drive the can with the MIL illuminated could also cause further damage to other systems of the car.
If you have some mechanical ability, and the ability to follow directions without jumping to conclusions, you could ask the nice fellows at the local discount parts store to retrieve the Diagnostic Trouble Codes for you. With the codes and descriptions in hand, refer to a repair manual for the car, and follow the proper diagnostic procedures first, then perform repairs. If you follow that order, you will most likely repair the problem rather than addressing the symptoms.

Happy Motoring

Answer 3

Your car computer monitors a number of systems within the vehicle.
Evaporative, Oxygen, catalyzer, vacuum, etc. When the computer detects that a sensor reading is outside preset parameters, issues a "pending code". If the fault continues or happens again, the computer alerts of the fault by lighting the malfunction indicator lamp, or MIL. The computer also stores the sensor information related to the fault for diagnostic.

A mechanic can use a scanner tool to retrieve not only the codes but also the engine parameters that went out tolerance and use the information to diagnose and repair the car. Once the repair is done, he/she can turn the MIL off and erase the fault code.

Answer 4

go to your local napa parts store, and ask for "The Tech's Edge" issue 07-01 its all bout OBD II systems its not a long read but will help you understand it...but there are many reason for it, and just hooking a cpu to it wont alwayz tell you what is wrong just tell the tech were to start lookingfor the prob....but in the end you are going to have to take your car some were to have it looked at

Answer 5

There are 1000 codes to trigger an OBD code.... most are sensors.... it could be anything that turns the light on.