Engine Control Module: Description and Operation

ENGINE CONTROL MODULE (ECM)
The ECM monitors the input/output signals (some signals at all times and the others under specified conditions).

When the ECM detects that an irregularity, it memorizes the diagnostic trouble code, and outputs the signal to the self-diagnosis output terminal.

The diagnostic results can be read out by the Scan Tool (ST). Diagnostic trouble codes (DTC) will remain in the ECM as long as battery power is maintained. The diagnostic trouble code(s) will, however, be erased when the battery terminal or the engine control module (ECM) connector is disconnected, or erased by the Generic Scan Tool.

NOTE:
1. When battery voltage is low, diagnostic trouble codes can not be read. Be sure to check the battery for voltage and other conditions before starting the test.
2. Diagnosis memory is erased if the battery or the ECM connector is disconnected. Do not disconnect the battery before the diagnostic trouble codes are completely read and recorded.