When the ignition switch is placed in the START position, a discrete signal is supplied to the body control module (BCM) notifying it that the ignition is in the START position. The BCM then sends a serial data message to the engine control module (ECM) that crank has been requested. The ECM monitors the park/neutral position switch and the clutch pedal position sensor. If the transmission is in Park or Neutral, or the clutch pedal is pressed, and there are no DTCs that inhibit engine starting, then the ECM supplies voltage to the control circuit of the STRTR relay. When this occurs, battery voltage is supplied through the STRTR relay to the X2-S terminal of the starter solenoid. The starter solenoid energizes, and supplies battery voltage to the starter from the B terminal to crank the engine.

Schematic Reference

Starting and Charging Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Starting System Description and Operation

Electrical Information Reference

1. Attempt to start the engine. Verify that the starter solenoid clicks.

⇒	If the starter solenoid does not click, refer to Starter Solenoid Does Not Click.

⇒	If the engine cranks slowly, refer to Engine Cranks Slowly.

2. Go to Circuit/System Testing.

1. Verify that the battery is sufficiently charged and that the battery cables are clean and tight. Refer to Charging System Test.

⇒	If the battery is not sufficiently charged, refer to Battery Charging.

⇒	If the battery cables are not clean and tight, refer to Fastener Tightening Specifications.

2. Using a DMM, measure voltage between the positive battery terminal and X1 terminal B at the solenoid as the ignition switch is turned to the START position. Voltage should be less than 0.5 volt.

⇒	If greater than the specified value, replace the starter solenoid cable.

3. Using a DMM, measure voltage between the negative battery terminal and the starter motor case as the ignition switch is turned to the START position. Voltage should be less than 0.5 volt.

⇒	If greater than the specified value, replace the negative battery cable.

4. Remove the drive belt(s). Refer to one of the following:

•	Drive Belt Replacement for the 4.3L (LU3) engine

•	Drive Belt Replacement for the 6.6L Diesel (LMM) engine

•	Drive Belt Replacement - Accessory for all other engines (w/o LU3 or LMM)

•	Air Conditioning Compressor Belt Replacement for all other engines (w/o LU3 or LMM)

5. Attempt to start the engine, with the drive belt(s) removed.

⇒	If the engine cranks, inspect the engine accessories and belt drive system for mechanical binding.

6. Attempt to rotate the crankshaft using a breaker bar, or other suitable tool. Verify that the engine is not seized.

⇒	If the engine is seized, refer to one of the following:

•	Engine Will Not Crank - Crankshaft Will Not Rotate for the 4.3L (LU3) engine

•	Engine Will Not Crank - Crankshaft Will Not Rotate for the 6.6L Diesel (LMM) engine

•	Engine Will Not Crank - Crankshaft Will Not Rotate for all other engines (w/o LU3 or LMM)

7. If all circuits test normal, replace the starter motor, or the starter solenoid (LMM 6.6L Diesel).

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.