[DRW1000]

I cannot see why the replacing the drive belt should have started this.

I also can't see why someone would replace the water pump to try and correct a code they could not read. (especially since on some years it is a 6 hour procedure).

In any event you took the first step in trying to read the codes. Unfortunately if you cannot connect to the PCM to get the codes everything you do is hit and miss. I would ensure that you are getting proper voltage to the OBD11 port. My personal code reader will give me a link error if the 12 volts (and return) are not present. There is a fuse that controls this.

I assume you have a 96 or later van but I don't think you mentioned the year.