Theory of Operation
The purpose of this test is to check the internal Engine Control Module (ECM) fuel system diagnostic (ASIC) for proper operation by falsely inducing a failure and looking for the proper ECM response. At key off, the diagnostic overwrites injector on time and falsely cycles the injectors. If the internal ECM detection chip (ASIC) detects the firing and sets an error than the diagnostic passes. This diagnostic initially only runs at key off. If the diagnostic failed at the last key off cycle, then it will also run at the next cranking event. If the driver stalls the engine (manual transmission only) at the same moment that the key is turned off this diagnostic could fail. When the diagnostic fails, the ECM will flash the ETC lamp.