Fault Phenomenon: Volvo L120 wheel loader cannot engage a specific gear (e.g., only forward, no reverse).

Troubleshooting Process:
– Checked solenoid valve: solenoid coil for the specific gear burnt or spool stuck.
– Checked harness: solenoid connector loose or wiring open circuit.
– Checked controller: TCU control unit faulty.
– Checked oil pressure: clutch circuit pressure leakage for that gear.

Root Cause: The solenoid valve controlling the reverse gear clutch coil burnt, unable to open the oil circuit, preventing the reverse clutch from engaging.

Required Parts: Replace transmission solenoid valve coil or spool.