Fault Phenomenon: Schwing S425 starts quickly when cold. When restarting after stopping (operating temperature), the starter motor turns slowly, sounds dull, and eventually fails to start.

Troubleshooting Process:
– Checked battery voltage: voltage sufficient.
– Checked starting circuit: no loose connections.
– Checked engine resistance: engine turns freely by hand.
– Measured starter motor current at operating temperature: found high current but low torque.

Root Cause: The internal carbon brushes of the starter motor wear excessively due to heat, causing poor contact.

Required Parts: Starter motor carbon brushes or motor assembly.