Will not fill with water. Voltage to water valve solenoid is about 75 volts. Voltage (120v) to everything else works fine. Can "hand" fill dishwasher and it will go thru its normal cycle except it will not fill with water when required.
Have not taken inside door panel off to check voltage there. Could it be the timer? Don’t know if it is the water valve because of the low voltage.
Here are your parts
http://www.appliancepartspros.com/partsearch/modelsearch.aspx?model=jdb5900aww
Most likely it is the timer.
Disconnect power from the unit.
Check the fill contacts on the timer, looks like 10 to 29.
Use your most sensitive meter scale, also short the meter leads together before starting so you know if there is a zero offset in the meter.
The contacts should measure 0 ohms.
If OK
Measure across the overfill switch.
It also should be 0 ohms.
If both the above and all the connectors in the fill circuit look OK then it is probably the fill valve.
I do not have resistance values for this valve.