Malfunction Indicator Lamp: Description and Operation

Also known as "SERVICE TELLTALE" lamp or "SERVICE ENGINE SOON" and "SERVICE VEHICLE NOW" lamps, the lamps are used to inform the technician that a malfunction of the CEC system has occurred. The "SERVICE TELLTALE" lamps are checked for proper operation while the engine is cranking, and will turn "OFF" after the engine is running.

Depending on the trouble code set, the "SERVICE VEHICLE SOON" or "SERVICE ENGINE NOW" lamp will come "ON" and stay "ON" while the malfunction is taking place. If a malfunction is intermittent, the service lamp that came "ON" will go out when the malfunction is no longer detected by the computer. When a "SERVICE VEHICLE SOON" or "SERVICE ENGINE NOW" malfunction is detected by the computer at the same time, only the "SERVICE ENGINE SOON" lamp will come "ON". Both lamps stay "ON" while the system is in diagnostic mode.