Reading Trouble Codes
Trouble code is set by ECM and describes a specific circuit fault. ECM compares each input sensor's signal with what ECM's memory has determined it should be. If sensor signal does not compare with ECM memory, the check engine light will illuminate and a trouble code will be stored.
Trouble codes may be obtained through the Assembly Line Communication Link (ALCL), which is located in passenger compartment. See Figure . Terminal "B" is diagnostic test terminal, and can be connected to Terminal "A" or ground to enter diagnostic mode.
Trouble codes are indicated by flashes of the CEL. For example, FLASH, pause, FLASH, FLASH, longer pause, identifies Code 12.