Damage to the downshift solenoid is indicated by the transmission not downshifting when the accelerator pedal is fully depressed, or by an erratic or rough gearshift.
Raise the front of the vehicle and secure it on stands. Drain approximately 1 liter of fluid from the gearbox.
Follow the wiring to the connector located near the battery and disconnect it.
Using large pliers, unscrew the switch and cover the hole with a rag.
Keep your finger on the solenoid plunger, secure the solenoid housing to the negative battery terminal, and while applying voltage to the switch contact from the positive battery terminal, verify that the solenoid plunger retracts.
Replace the solenoid if there is any doubt about its condition.
Apply sealant to the threads of the solenoid before installing.
After installation, check the fluid level and top up if necessary.