Remart Auto Parts Blog

The Check Engine Light (which is actually the Malfunction Indicator Lamp or MIL) alerts you when a problem occurs in the engine control system. Depending on the nature of the problem, the Check Engine Light may come on and go off, remain on continuously or flash. Some intermittent problems will make the Check Engine Light come on only while the fault is occurring. When the problem goes away, the Check Engine Light goes off. Other types of problems will turn the Check Engine Light on, and it will remain on until the fault is diagnosed and repaired.

The Check Engine Light can be annoying because it seems to have a mind of its own. The Check Engine Light also tells you nothing about the problem. It might be something serious - or it might not. There is no way to know until you diagnose the vehicle. So you don't know if you should stop immediately or ignore the Check Engine Light and keep on driving.

If no other warning lights are on, and the engine seems to be running normally (no unusual noises, smells, vibrations, etc.), you can assume the fault that is causing the Check Engine Light to come on is probably minor and won't hinder your ability to continue driving. But if other warning lights are on, you should stop and investigate the problem.

When the Check Engine Light comes on, a diagnostic trouble code (DTC) is recorded in the on-board computer memory that corresponds to the fault. Some problems can generate more than one trouble code, and some vehicles may have multiple problems that set multiple trouble codes.

Click Here for a list of generic OBD II Trouble Codes.

SETTING TROUBLE CODES

In most older vehicles (those made before 1996), disconnecting the computer's power source or disconnecting a battery cable erases fault codes and turns off the Check Engine Light, at least temporarily. If the problem persists, the code will reset and the Check Engine Light will come back on. But on many newer vehicles, you do NOT want to disconnect the battery because doing so can wipe out the computer's memory settings. This may affect the operation of the transmission, climate control system and other functions.
In 1996 and newer vehicles, a scan tool or code reader must be used to erase codes and turn the Check Engine Light off.

READING FAULT CODES

If your Check Engine light is on, you need to read the code(s) that are causing it to come on with a code reader or scan tool. The tool is plugged into the vehicle diagnostic connector. The 16-pin connector is usually located under the dash near the steering column. When the ignition is turned on (don't start the engine), the tool will display a number that corresponds to a fault code description. The code will tell you which circuit or component is involved, but the code by itself will NOT tell you which part to replace. That requires more diagnosis.

OBD II CHECK ENGINE LIGHT DIAGNOSTICS

Prior to OBD II, fault detection was mostly limited to "gross failures" within individual circuits or sensors. The first generation systems were not capable of detecting misfire, converter problems or fuel vapor leaks. OBD II changed all of that by adding the ability to monitor these things so emission problems can be detected as they develop.

OBD II still uses the Check Engine Light to alert the driver when a fault occurs, and it still stores trouble codes that correspond to specific kinds of problems, but it adds the unique ability to track problems as they develop and to capture a snapshot of what is going on when a problem occurs.

Almost any emission problem that causes hydrocarbon emissions to exceed 1.5 times the federal limit can cause the Check Engine Light to come on with OBD II - even if there is no noticeable drivability problem accompanying the emission problem.

OBD II not only monitors the operation of all the engine's sensors and systems (fuel, ignition, EGR, evaporative emissions, etc.), it also monitors the operation of the catalytic converter and can even detect engine misfires! Anything that could possibly affect emissions is monitored by OBD II, including a loose gas cap!

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At Remart Auto Parts we are not mechanic's nor do we validate or warrant the information included in this blog. If in doubt about any information included in this blog, please consult a certified mechanic before attempting any vehicle repair. To view complete information about this disclaimer and the source and origin of content on the remartautoparts blog, click here.