It gets kinda bogged down in the test procedure,but to diagnose if you have a bad ldp it goes like this..use a hand held held vacumn pump and apply 18 in. of vacumn to the svst port vacumn tee. The vacumn should hold, if it doesn't check all the lines are good before replacing the ldp. Then it goes on to actuate the ldp solenoid with a drb with the ignition on .The vacumn should drop,and if it doesn't replace the ldp.
Apparently the ldp solenoid is a 12 volt circuit and you should be able to isolate and test the solenoid if needed. You should hear a clicking sound, and when acuated it should drop the vacumn as stated above. To further test the solenoid circuit you'll need to get familiar with the wiring diagrams section in the manual you have. The fused ignition supply cavity two to ground with the connector disconnected from the ldp should be more than 10 volts with the key on.
Further, to test the circuit from the pcm to the ldp , key off, disconnect the black connector to the pcm and read from the C10 pin to the cav3on the ldp connector. If the 97-98 wiring layout is the same it should be a DG/RD wire. It should be less than 5 ohms.
It goes on to test for a short to ground, which with your given code is probaly unlikely. But if you need me to I'll relay the info. But to test the vacumn portion of the ldp this work around may work. It never gives actual vacumn readings and to test the system further requires pressurising it with a chrysler gizmo. Hope this helps.
Move over bear.I'm tired of working on the jeep
Links to axle rebuilds, mount replace,a/c box rebuild,ect in history section of my profile page