TM10-3930-660-20 Table 2-3. Mechanical Troubleshooting (Cont'd) . MALFUNCTION TEST OR INSPECTION CORRECTIVE  ACTION — Step 2. Check for defective hydraulic joystick control valve. Replace hydraulic joystick control valve if necessary, para. 18-12. 53. FOAMY HYDRAULIC OIL Step 1. Check for water in hydraulic oil. Determine where water entered system. Change oil, para. 5-10. Repair leaks as necessary. Step 2. Check for low oil level. Add oil as necessary, LO10-3930-660-12. 2-50