Ignition Output Signal: Description and Operation

COMPONENTS
The ignition control system consists of the "EI" assembly (coils, module, and CKP sensor), ECM and connecting wires. These circuits perform the following functions:

"EI" reference
The CKP sensor sends a signal to the ICM which generates a reference pulse which is sent to the ECM. The ECM uses this signal to calculate CKP and engine speed (also used to trigger the injector).

Reference ground (GND)
This wire is GNd through the module and makes sure the GNd circuit has no voltage drop between the ICM and the ECM, which if open, could affect performance.

Bypass
At about 400 revolution per minute, the ECM applies 5 volts to this circuit to switch spark timing control from the ICM to the ECM. An open or grounded bypass circuit will set a diagnostic trouble code 42 and the engine will run at base timing, plus a small amount of advance built into the ICM.

IGNITION CONTROL (IC)
The ECM uses this circuit (when bypass voltage is applied) to trigger the "EI" module. The ECM uses the CKP to base its calculation of the amount of spark advance needed under present engine conditions.