DIAGNOSE – The “CHECK ENGINE” LIGHT CAME ON
by Jim Miller
The “Service Engine Soon” or “Check Engine” light comes on while the engine is running.
The vehicles electronic control unit constantly monitors and adjusts various engine parameters. If the control unit detects a failure in one of the connected circuits, it will illuminate the malfunction indicator lamp and wll store a diagnostic trouble code in its memory that corresponds to the failed circuit. If the malfunction indicator light is on, the computer has detected a malfunction in the engine management system.
The diagnosis of the symptom requires interfacing with the on-board computer and retrieving the stored diagnostic trouble code. Manufacturers troubleshooting procedures are then used for the specific trouble code that was retrieved. A special hand held computer, usually referred to as a scan tool, is required to interface with the computer. However, some manufacturers use the malfunction indicator lamp to flash a series of blinks to indicate the specific code. On these vehicles, diagnostics are usually entered by grounding or connecting a pair of diagnostic connectors. Once connected, the computer transmits the stored code(s) to the lamp. The lamp flashes are counted to determine the corresponding code. You will need to refer to the manufacturer specific repair manual to determine the type of system utilized on your vehicle.
PRECAUTIONS, TIPS, and NOTES
Working on the computer system requires a good working knowledge of electrical system theory and the proper testing equipment. The computer system can be damaged by using the incorrect test procedures. There are relatively inexpensive test equipment available to retrieve the diagnostic codes from the most common vehicles. Consult your auto parts store for availability.
is a lifelong fan of Dodger Baseball and used to race sprint cars in