I have a 2001 4 cylinder LX sedan, and have had the flashing light and p1738 code, so I know I've got to replace the pressure switch ... but I can't do it yet.
I have found a way to cope with the problem, so maybe this can help others with the similar situation. I noticed that the problem wasn't constant, and seemed to only occur when the car had been in cold temps for a while, like 8 hours of work or overnight. So, just by chance, I decided to let the car warm up on a particular morning, and with foot on brake, I went through the gear positions, pausing for a minute or so at each gear, for about five minutes or so.
When I do this, I have no flashing light, no code, and the car shifts normally as I drive off. I suspect that going through the gear positions while the car idled allowed the trans fluid to circulate better before driving off. Now, the car has had the 3x fluid drain before this, and I did use Honda fluid, and it's full, but I bought this car used, so I had no knowledge of how the former owner treated it. So this might help anyone with the flashing 'D4' when it comes up..