What to Check First When a Check Engine Light Comes on
- The very first thing to check when the "Check Engine" light (also known as the malfunction indicator light) illuminates on the instrument panel is the code. A computer or scan tool must be hooked up to your vehicle, and the pertinent information about the vehicle must be logged into the scan tool. Newer scan tools don't require much information concerning the vehicle, if any at all.
So when the MIL comes on, simply checking the fluids, air filter or any other common maintenance component---although a good preventive maintenance practice---is ineffectual. The fluids for the vehicle (such as oil, transmission and coolant) employ their own service indicator lights that will illuminate when there's a problem.
Most diagnostic trouble codes (DTCs) that trigger the MIL deal with emissions or internal modules or sensors. Because of this, and because there are hundreds of DTCs that can cause the MIL to light, the quickest and most effective way to diagnose the problem is the have the electronic control module (ECM) scanned. - Electronic control modules have been integrated with vehicle systems since the late 1970s. By the early '80s with the implementation of OBD, they were mandated by law. However, each car manufacturer could design their own style and placement of the ECM. This caused many problems for diagnosing the MIL. Different plug-in adapters were often required for different makes and models, and the location of the diagnostic link connectors were not standardized. Some models even employed the MIL to flash in numeric sequence to communicate the code.
- The implementation of OBD II in 1996 standardized the MIL codes and placement of the diagnostic link connector. In addition, the same plug and outlet for every vehicle made was standardized.
- When the MIL lights up on the instrument panel, something has gone wrong in the vehicle, and it's trying to let you know. While most auto parts stores and repair stations carry OBD II scanners, they often offer to scan the vehicle for free. In addition, portable scanners are now available for the do-it-yourself mechanic.
Vehicles equipped with OBD before being manufactured in 1996 may find they have to pay the service station or dealership to discover the problem with the vehicle. This is because the scan tool may require several adapters and computer chips to retrieve the information. - Cheating the MIL is futile. Resetting the code is most likely only going to result in the light coming back on. Sometimes it takes a while for the computer to retest itself; other times, on hard codes, it will light right back up. Not all codes are hard codes and can be fixed quite cheaply, but the best thing to do when that "Check Engine" light flashes on is to have the computer scanned and take all the guess work out of the problem with your vehicle.