Est Signal

When in the EST mode, ECM controls EST and compensates for all driving conditions. If ECM has an internal failure of the EST system, this will cause ECM to operate in an ignition timing back-up mode. The "SERVICE ENGINE SOON" light will illuminate. If the EST fault is present the next time the engine is started, Code 42 will be set. An open or grounded EST circuit will cause engine to stall. Engine will restart; however, engine will stall again once by-pass line tries to reactivate EST mode.