01 Honda Odyssey is automatic, but D4 starts blinking and I have to manually shift between gears, why is this? ?

You must first check the auto transmission fluid leaving the car idling in park and open hood and take out the auto transmission dipstick, take a snot rag and wipe it off and stick back in, count for 3 seconds and pull the stick out and look to see where the transmission fluid is at.  It must be there between the two lines.  If it is,THEN "that is not the PROBLEM." One item ruled out. Otherwise I don't know where to go with it as that is usually the FIRST THING YOU CHECK....because most people don't do that and it gets  real low and you don't go.  Maybe that is what the complaint is by the car.  I have never run into the issue because my fluid is always right.

Try it. It might be THAT SIMPLE. 

It's a 19 year old vehicle so it could be anything, minor or major.  First off, have you checked your fluid level?  Apparently noone who has answered knows this, but 1999-2003 Honda Odysseys have a well-known high transmission failure rate, even when they were new. There was even a TSB from Honda about it. Honda extended the warranty period on the transmissions. They also  made "improvements" to transmission but even those would eventually have the issues. I remember owners hoping their transmissions would fail before the extended warranty would end on theirs so they could get a new transmission. If yours is original, count your blessing that it made it this far. 

means a transmission code. find local shop at ATRA.COM for them to pull the code. possible its a solenoid code. if it comes up as a 741 code don't be surprised if it's recommended that its a torque converter that's gone bad. Honda had big problems with torque converters between 98-07

This Tom guy (friend of David Goldberg) claims that gov't will extract adrenochrome from truthers under Project Zyphr.

Gov't identified the truthers under Project Pogo.

Project Pogo was to gather info on dissidents when they commented/watched videos of Alex Jones / QAnon / Adam Green / etc

Drone with scopolamine will drill a hole in your window; once gassed you will come out to them yourselves. This is done @4 AM during the night (also electricity was turned off for your block / region )

This Tom guy begged people to leave to South America 'cuz of CONTROL GRID...

I think it's better to hide in the woods of Alaska. What do you think?

The remaining people will be chipped when they sign up for food

Hell... even saint Vyacheslav Krasheninnikov said that Americans will receive mark of the beast because everything is like on your palm (you can't hide anywhere from the CONTROL GRID)... So, I was told to tell you this so that I won't be punished by God. Sorry, if the warning came out wrong

Police will stop you at checkpoints to see if you're chipped (aka vaccinated)

Chipped will be influenced (by super computers) ..to receive World Passport (grey plastic card with no name on it)... but when they stretch their hands to get it …gov't clerk will press secret button to administer the unforgivable green 666 tattoo by isotope rays..

This Tom guy and saint Vyacheslav Krasheninnikov both said that once you hide: no documents / no electronics / etc. so that nothing holds you back and you won’t go back into the city ‘cuz police will stop to chip you if you decide to go back. You have to live off grid; it’s tough but it’s the only way; forgive me.

Antichrist will also release prisoners/insane asylum people to mark everyone. Police will mark people on highways. Food stores will mark people who steal marked food because in order to swallow marked food one has to have triple stranded DNA. Mark changes your DNA from two strands to three strands so that you can't die and demons will live inside you forever (or so they think). Angel will cut marked people's heads clean off at the end of Apocalypse. If you reject mark of the beast, then your direct ancestors will go to heaven (according to saint Vyacheslav Krasheninnikov); forgive me.

It is NOT usually very serious! But TRANNIES need LOVE just like the ENGINES DO! The TRANS needs FLUID CHANGES and perhaps you only need a VEHICLE SPEED SENSOR or a TRANS speed sensor! It is TRYING got protect itself from HARM! GET THE CODES READ at ANY AUTO ZONE but do NOT necessarily get AUTOZONE PARTS! Get it from the DEALERSHIP or ON LINE cheaper! REALLY!

Most imports will have the "D" or "N" shift indicator light flash when there are transmission codes for the electrical transmission operating system. The problems are usually the transmission input or output speed sensors or a shift solenoid malfunction. You need a $3000 mechanic scan tool to read the tranny codes and read the transmission data to determine the problem. OBD II code readers do not work to read tranny codes.

i would have a mechanic check it out

The D4 light blinks  to let you know the transmission needs to be serviced. This doesn't necessarily mean your transmission is needs an overhaul, but have it looked at ASAP.

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(p.s. a clever lad could have googled this problem and found the answer in seconds. An even more clever lad would have looked in the owners manual. It's a free download from Honda).

You have a very serious transmission problem. Take it to a professional.