Starting System Circuit Description (LP4/L21 Engines)

Starting System Circuit Description (LP4/L21 Engines)

Battery voltage is available at the ignition switch at all times through the CKT 642 (RED) from MaxiFuse(R) block 2. Battery voltage is available to the starter relay contacts at all times through CKT 2 (RED) from fusible link M off of the starter. Placing the ignition switch in the START position closes the contacts in order to apply voltage on CKT 5 (YEL) to the CRANK circuit breaker in the IP fuse block. If equipped with an automatic transmission, and shift selector is in the NEUTRAL position, the crank request will be recognized by the PCM, and the PCM will provide a ground path for the starter relay coil and close it's contacts in order to provide voltage to the starter solenoid in order to crank the engine. If equipped with a manual transmission, the the clutch pedal must be fully depressed, as well as the shift lever being in the neutral position, in order for the PCM to recognize the crank request signal.

The starter relay energizes when voltage is applied to the coil. Voltage then applies to the starter solenoid winding terminal S through CKT 6 (PPL). Battery voltage is also available at all times through CKT 1 (BLK) at the starter solenoid terminal B. Current flows through the hold-In winding to the mechanical ground at the solenoid when battery voltage applies at terminal S. Simultaneously, current flows through the pull-In winding and the starter motor to the starter motor's mechanical ground. The combined force of these windings overcomes the force of the return spring. The combined force of these windings also pulls the starter's plunger in order to engage the starter with the flywheel drive assembly through the shift lever. The engine starts to turn over. The plunger actuation also operates a contact in the starter solenoid. The contact in the solenoid closes in order to apply battery voltage directly to the starter motor. The pull-in winding no longer has a voltage drop across the coil when the battery voltage applies directly to the starter motor. The current then ceases to flow. The starter solenoid remains engaged due to the current flow through the hold-in winding alone.

The starter motor continues to operate until the ignition switch returns to the RUN position. Voltage is removed from the starter solenoid terminal S when the ignition switch remains in the RUN position. Voltage still remains at terminal B. Both the hold-in winding and the pull-in windings now oppose one another. The plunger returns to the disengaged position through the operation of the return spring. This condition operates the contact in order to remove the battery voltage from the starter motor. The motor stops. Both windings also de-energize. This plunger operation also retracts the starter from the flywheel drive assembly and the engine operates on the engine's own power.