Est Signal

The DIS ignition module sends a reference signal to the ECM when the engine is cranking. If the engine is under 400 RPM, The DIS ignition module controls ignition timing. When engine speeds exceeds 400 RPM, the ECM applies 5 volts to the by-pass line to switch spark timing to ECM control.

An open or grounded EST circuit will result in engine operating in a back-up ignition timing mode and the "SERVICE ENGINE SOON" warning light will come on. If EST fault is present the next time engine is started, Code 42 will be set.