Quick question about measuring ATF level.

[carman850]

When I measure ATF fluid level, service CD says I should put transmission into "P", but doesn't say if I should shut down the engine or not.

I changed my transmission fluid by myself last week, now the car hums and vibrates when I stop the car with level in "D", I filled the ATF between min and max when engine temp was 80C, but I did that when the engine was shut down, don't if that was right or not.

Mine is a 92 400E, I use Mobil-1 ATF.

Thanks.