Electronic Control Module (ECM)
The ECM constantly examines input information from various sensors to configure output signals to fuel and ignition system components. ECM monitors sensor input signals, and can diagnose out of range signals to self-diagnose faults. A faulty signal will cause ECM to alert vehicle operator by switching on "Service Engine Soon" light. Records of faulty signals will be stored in ECM memory and may be outputted in the form of a signal code to identify component or problem. Stored fault code output may be requested by jumping a circuit of ALDL connector. Codes may be read by counting "flashes" of the "Service Engine Soon" light or by a "Scan" tester display. The ECM is a basic design item used in various General Motors vehicles. To adapt it to specific applications, each ECM is fitted with a replaceable "MEM-CAL" calibration memory chip. Ensure vehicle is equipped with correct "MEM-CAL" chip. Manufacturers may update "MEM-CAL" memory chips to service driveability concerns. Replacement ECM's often are delivered without "MEM-CAL" chip installed.