You can pull ther vac right at the outlet line of the SOV.. [ green line]. That goes to the cable element and is , as Doc says . more likely the problem than the SOV..

For testing , the system basically is this :

When cold and first drive cycle, the ECU sends a dc signal to the solinoid coil of the SOV. That opens the valve to allow engine vac to flow through it to activate the cable element at the trans.
[ which holds/delays the shift point ]

So , for testing, first see if you have vac at the SOV inlet line from the engine. IF not check that line back to the engine for a break/unplug.
If OK , then check the vac hold of the outlet line..
The next test is to "T" a vac gauge into the outlet line of the SOV
and watch the gauge w/test drive [ I tape gauge to windscreen]
If gauge shows vac for this test, you know that the SOV is recieving a sig from the ECU and the SOV is allowing vac flow..
If not , these two can be further tested by checking the 2 wire connector w/meter for power and gauge for flow with power
to tell if it is the SOV not recieving a sig or the SOV being energized, but not opening [ allowing flow],,
The code remedy/fault chart pushes you in the direction of shorted/open SOV, but that is rarely the case...
I only mention this cuz I see lots of members buy an SOV when not needed... plus knowing the basics of each system gives one
some ammo to fiqure the possibles out...

Also, As many of these are now being bought as used cars, it is good just to check the vac lines for blockage as many guys hate the delay and they put a 'BB" in the line [usually around the SOV in/out connectons] ...me being one