by B. L. Babb

Created on: November 05, 2009

To understand the CHECK ENGINE light it is necessary to understand why it is present.

As cars transitioned from carbureted machines to fuel injection and with the push for fuel economy, the car became computerized. An Electronic Control Unit or ECU monitors and controls many aspects of a vehicle as it moves along the country's highways and byways.

This change to computerization also allowed for the creation and use of on board diagnostic software. This software was initially utilized to help clean the air. It would light a lamp on the dashboard indicating the computer had received a parameter that is out of specification for that system or component.

The SERVICE ENGINE or CHECK ENGINE light is a dashboard warning light that hopefully only illuminates during that brief period when you are initially starting your car.

If it comes on while driving, do not panic. It is not possible to tell from just this light if the problem is of a serious nature or a minor issue. Listen to the engine. If it sounds normal, your best bet it to get your car to a shop in the near future. If the car engine is not sounding normal, consider immediately parking the car or heading directly to a shop within a reasonably short distance.

What could be a minor issue? Many new vehicles today require that the gas cap be tightly fastened after refueling. If this is not done, within a few starts the CHECK ENGINE light will come on causing a sinking feeling in the pit of your stomach and wallet.

Tightening the gas cap may not clear the light, even if it was the cause of it to begin with. Some vehicles may require 20-50 starting cycles before the computer clears the code while other cars may never clear it, even if the problem has been corrected.

Does a misfire code in conjunction with an O2 Sensor code mean you must replace the O2 Sensor?

Typically a misfire can be caused by a problem ranging from a malfunctioning spark plug, injector, plug wire, or coil (however, this is only the short list.) This malfunction can then lead to raw gas being dumped into the exhaust because the cylinder is not firing or not firing correctly leaving unburned gas to flow into the exhaust system where it can foul the O2 sensor and click on a second code. In this case, correcting the misfire will correct the O2 code, so O2 sensor replacement most likely will not be necessary. An exception to this is if it is allowed to occur for an extended period of time, the sensor could ultimately be damaged.

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