Accessing and Reading Diagnostic Trouble Codes

The Electronic Control Module (ECM), is really a computer. It uses sensors to look at many engine operating conditions. It has a memory and it knows what certain sensor readings should be under certain conditions. If a sensor reading is not what the ECM thinks it should be, the ECM will turn ON the CHECK ENGINE light on the instrument panel, and will store a trouble code in the memory. The trouble code tells which circuit the trouble is in. A circuit consists of a sensor (such as the coolant sensor), the wiring and connectors to it, and the ECM.

To get a trouble code out of the ECM, it is necessary to jumper the BLACK wire and the BLUE/YELLOW wire at the ECM check connector, located under the hood by the battery.