I went through the entire thread more or less my car recently is having a similar problem.
I have Honda City Vario AT 2005.
When you start the car up in the morning , the D is blinking and apart from R , no other gear e.g. S or L or D works . I have to wait for 5-10 mins and then the car starts to drive in D . And it has a weird sound as well , like releasing of air from a high pressure vessel.
Then again when the car is switched off , depending on the duration for which the car remained switched off , it starts to drive in D normally , however if the duration is more than an hour , then again the D light is blinking and it does not drives straight away. I have to wait again for 5-10 mins. Meanwhile , during the drive I don't experience any problem in shifting between gears.
I went to Honda Center and they diagnosed three sensors malfunction and they need to be replaced . ( Unfortunately , I forgot to note down the exact names and the error codes )
I went to another mechanic ( for second opinion) and he told me that there is some sort of " kachra" in the transmission plate and if I get it cleaned , there wont be a problem anymore.
I had my gear oil replaced on 3rd September so I dont think that there is anything related to gear oil .
It is indeed very perplexing situation as in this thread , already I believe Tayyab has tried the sensor replacement. I want to first ascertain that what is the exact problem and then go with the recommended repairs.
tons of thanks in advance. Everyone's help will be appreciated .