We have a 4 stop DMC-1 with an intermittent problem,the door stays opened, PI flashes and nudging closes it. Mechanical is fine, checked EE /SE variables O/K and the CLC has door close command. It will also go to a floor and not open the door sometimes. The CLC shows a open command and the door operator show an open command, no voltage across DA1/DA2, DA1/GND 82VDC, DA2/GND 79VDC, 150 VDC at door operator board fuse, the manual open/close buttons do not work this has a new door board. The car will then run to another hall call and not open the door, time out and run again.

The only way to clear the problem is to cycle the main power as the reset on the door board will not.

Sounds like a software issue what gen software in door board. You said new fx3?
How old is the unite?
Dmc always flashes pi when on nudging.

Possibly the parameter for the door open pick up (backlash speed?) is just too low and not enough poop to move the doors? Do they stall at near fully open? Hold them back at or near DOL and see if they'll pull through. Overall how do the door speeds look? Maybe torque is too low? Like Fred said, Doors open, the PI flashing and the car off line is definitely in the category of doors failing to close in the allotted time. Door ramps'l do it too, bad brushes'l do it. Broken collar on DOL/DCL limit? What is the Door Fault #?
Be sure to let us know what you found when you get it!

Belts, always where I start, and usually where I end. See if the belts are loose, sometimes service mechanics crank the torque to "fix" an issue and a loose belt is torqued through, finding a DCL, but not the gate, or vice versa. Also ran into one such creature that car gate and DCL made up, but now the hoistway doors wouldn't make up.

I totally agree with Silly, any DMC Door problems, replace the Belts first.

I ran into this a few times. If its a door board from an older revision you should replace the board. There are some resistors in the top left corner that are problematic and causes the doors to fail to open/close.

Not enough info. How old is this DMC? Is that a 6300 BP1 CLC board? Does the door lock clear the lock box at that floor? Is that a repaired door board? Does that door make the limits? Did you get a new door scan and save it to memory?
Are the door adjustments too low?