If a malfunction of the automatic transmission is detected, first of all check the level of the working fluid (refer to section Checking the automatic transmission oil level). If the level is low, check all seals. Carefully inspect all hoses related to the transmission fluid, as well as the coolant, and make sure that there are no signs of leaks. The only thing you can still do yourself is to check and, if necessary, replace the sensors related to the operation of the box (temperature and rpm). Before replacing any sensor, read fault codes from the memory of the control unit.
In case of a relatively serious breakdown, the box control system will switch to a safe operation mode, while entering the appropriate code (or codes) to the memory of the control unit. Codes can be read using special equipment.
If not, determine the nature of the problem (electrical or mechanical).
Do not attempt to remove the box, as the diagnostics are performed only on the box installed on the engine.