01 Cefiro VQ30DE - Gearbox Problem?

I was driving as usuall suddenly my car slow down and was not moving at normal driving condition. When I press the accelerator, the rpm went up to about 4000 but the car just moving about 30-40kmh. I drove the car slowly about 3-4km to a workshop (doing about 15-20kmh @ 2000rpm). The mechanic tested my car and said it could be the gearbox problem. Not knowing the actual fault, the mechanic changed the transmission fluid and tested the my car again. It performed normal and the mechanic told me to use the car to see whether the problem persist again. As I was driving, about half an hour later the problem came back. I also noted that one of the radiator fan on lefthand side was not running. (Only one was running)Can anyone give some advise what could be the probable cause of the problem and how to repair it. I will very gratefull for your help. Milleage: 85000km. Thank you.

I was driving as usuall suddenly my car slow down and was not moving at normal driving condition. When I press the accelerator, the rpm went up to about 4000 but the car just moving about 30-40kmh. I drove the car slowly about 3-4km to a workshop (doing about 15-20kmh @ 2000rpm). The mechanic tested my car and said it could be the gearbox problem. Not knowing the actual fault, the mechanic changed the transmission fluid and tested the my car again. It performed normal and the mechanic told me to use the car to see whether the problem persist again. As I was driving, about half an hour later the problem came back. I also noted that one of the radiator fan on lefthand side was not running. (Only one was running)Can anyone give some advise what could be the probable cause of the problem and how to repair it. I will very gratefull for your help. Milleage: 85000km. Thank you.

First run the self diagnostics as the problem is ON. In 3gen maxima the tranny diag runs at every startup; mode switch lights work as error code status indicator.

Your symptom is like tranny dropping into 'safe-mode', google for this. This happens if (rpm) sensor or (?) signal fails to reach the A/T computer. Very often one gets faulty diagnosis (read: nicey pricey), when issue most probably is one connector pin loose or gnd contact gone - take care dont accept $$$$.$$ tranny swap.

Read tranny link & contact maint -pages below to get the idea...

Dear Nahkapohjola,

Thank you very much for your reply. Will check per your advise.