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Release Date: 2009-04-26 08:14:23

Help! My Check Engine Light Has Come On

So your car MIL (Malfunction Indicator Lamp) has lit up! To paraphrase "The Hitchhiker's Guide To The Galaxy",

DON'T PANIC!

This indicator lamp is controlled by an electronic management system fitted to modern cars called OBD2 (or OBD-II). OBD is an acronym for On Board Diagnostics. The OBD2 system is designed to give you early warning of malfunctions and allow you to address these. There are two possible ways in which the lamp can come on.

• In the normal course of starting the engine, the lamp will illuminate, then go out after a few seconds. If the lamp does not go out, or comes on in the middle of normal driving, the On Board Diagnostics system is letting you know it has detected a fault. This does not mean you need to stop the car and turn the engine off. It does mean you need to have the vehicle checked as soon as is practicable. There are literally hundreds of possible reasons for the light coming on, some as simple as leaving the fuel filler cap loose after refuelling.
• The lamp may start flashing whilst you are driving. This is potentially a more serious matter and normally means a severe engine problem which could cause damage if left unattended. There is still no cause to panic. The fault does not render the vehicle unsafe to drive. There is however a requirement to rectify the fault as soon as possible to prevent costly engine damage.

In many respects, this is an unsatisfactory situation. You know you have a problem but you don't know what it is, or its severity. What repair shops would like you to do is to let them check the vehicle with their OBD scanner. This is a costly exercise, even when the cause is simple and easily rectified by the average driver.

More recently, another option has become available for the home mechanic. It is now possible to buy an inexpensive unit which can plug directly into a PC, a laptop, or a handheld computer. With suitable software, it is possible to interrogate the OBD2 system and find out why the fault light has come on. If you can easily rectify the fault yourself then you've saved on the cost of a repair bill. If fixing the fault is beyond your technical skills and you still need to visit the repair shop, at least you can tell them what the problem is. This should also save you money by cutting down on the time needed for diagnosis.

However, being able to read fault codes is only one facet of the OBD2 system. There is so much more to it than that. If you have a carputer installed in your vehicle, you have the ability to have your carputer permanently connected to your OBD2 system. This gives you the facility to interrogate the system for all the variables it monitors, everything from speed and engine revs, to manifold pressures, air flow rates and a whole host of other data.

For a fuller explanation of OBD2 and fault codes, go to?www.my-car-computer.com/obd2.html, where you can also find out all you need to know about building and installing a carputer.