That Darn Pesky "Check Engine Light"

Check Engine Light

The computer’s function is to minimize pollution. It has many sensors and solenoids it can actuate (cause to turn on and off) to monitor, adjust and fine tune your car to minimize its pollution.  When there is a problem with a component in the computer control system, the computer illuminates the “Check Engine” light or it illuminates the “Picture” of an engine.  For the rest of this article, I’m going to refer to these lights as (check engine light) CEL.

When you see the CEL on there is a problem.  I shake my head, and quiver when I hear a customer say, “The last mechanic said there was nothing wrong with my car.” If there was nothing wrong, the light would be off!  I am also amazed when I’m told by a customer that the last mechanic said they did not need to repair the problem.  Later you will know why this is a bad, bad idea.

When a car is here because the CEL is on I use a tool called a  “Scanner”  to connect to your computer.  One of the displays on my scanner is a number which is referred to as a code.   This first step is referred to as “Pulling a Code.”  Each problem for which your computer turns on the CEL has an associated number or “Code.”  Pulling a code does NOT tell me what part is bad- it tells me what area in the computer control system is/was malfunctioning.  I then print out a diagnostic chart related to this code, and I print out an electrical schematic for the problem area.  With these two print outs, and some other diagnostic tools, I can diagnose your computer system’s problem.  Most of computer diagnostics take between 30 and 45 minutes.

Three Possibilities When Your CEL Is On:

1.        The problem will affect performance.  For example, if your ignition coil went bad your car to run rough.

2.       The problem will NOT affect performance.  For example a bad gas cap allows the gasoline fumes from the gas tank to leak into the atmosphere.  A bad gas cap does not affect performance but it does pollute the air.

3.       The part which is bad will not affect performance, but left unchecked, it will cause another part to go bad.  For example, a bad oxygen sensor, on most cars, will not affect performance, but if it went bad and you left it on your car it will cause the catalytic converter to go bad.  Replacing the oxygen sensor when goes bad saves you a lot of money. 

Here’s another reason to repair a part that will not affect performance

Let’s say your last mechanic said the CEL is on because of a bad gas cap.  You choose not to replace it since it will not affect performance, nor will it cause any problem to any other part in your car.  That is correct….. but, three months later the oxygen sensor goes bad.  You don’t know it went bad since the computer does not have a ‘second’ CEL, nor can it make the CEL get brighter to inform you that another part went bad.  By the time your car is not running well, and you bring it in for repairs, you’ll need to replace the oxygen sensor and the catalytic converter.  Therefore, not replacing an inexpensive part, cost you hundreds of extra dollars in repairs.

Can The State of Illinois Make Me Fix MY Car?

Cars 1996 and newer need to have an emission inspection every two years.  These inspections, to be official, can only be done by a State of Illinois Emission Center, and you may only go for an inspection after you receive a notice from the State of Illinois.  If you pass the inspection, the test center notifies the Secretary of State, and your license plate is renewed. 

If your CEL is on, you’ll fail the emission test, and the State will not renew your license plate until you repair the car or they issue you a waiver.  Basically, waivers are only issued after you have spent money trying to repair you car.