Fault Phenomenon: Komatsu 930E mining truck during downhill grades, the braking resistor grid fan does not run, causing the resistor to overheat and trigger protection.

Troubleshooting Process:
– Checked contactor: fan motor contactor contacts burnt or coil burnt.
– Checked thermal overload relay: thermal overload protection tripped and not reset.
– Checked motor: fan motor windings burnt.
– Checked control: PLC output signal normal.

Root Cause: The control contactor for the braking resistor cooling fan failed due to frequent switching and high current impact, causing contact welding or coil burnout.

Required Parts: Replace fan motor contactor.