1. Check Battery Charge: Ensure the battery is fully charged and inspect battery terminals for cleanliness and tightness.

2. Inspect Electrical Connections: Check starter motor circuit connections for looseness or damage, especially power and ground cables.

3. Examine Starter Relay: Verify proper operation of the starter relay, ensuring it is not burnt out or experiencing poor contacts.

4. Inspect Starter Motor: Check the starter motor itself for damage or wear, focusing on brushes and armature.

5. Check Starter Drive Gear: Inspect engagement between the starter drive gear and engine flywheel ring gear, ensuring no damage or looseness.

6. Inspect Control Circuit: Check the starter control circuit, including switches and relevant sensors, to ensure proper signal transmission.

7. Clean and Lubricate: Clean and lubricate moving parts of the starter motor to ensure smooth operation.

8. Check Ground Connections: Ensure the starter motor ground connections are secure and free from corrosion or looseness.

9. Testing and Replacement: Conduct electrical tests as necessary or replace the starter motor or components if needed.

These steps will help diagnose and resolve issues with the excavator starter motor.