Why can't i get comm.w/pcm on A 2000 Dodge Grand Caravan 3.3 L. w/any scantool?

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In order for this 2000 Dodge Grand Caravan 3.3L to pass smog, it must communicate w/obd II. when a scantool is hooked up to the DLC, it prompts, no communication w/ ecm. where can i find the information to diagnose this situation? I have tried Mitchell, however, the diagnostic steps given have passed. Ive got 2.5 volts to CCD bus + and -. both grounds at DLC are less than 5 ohms. I got power, where can i find more info. on how to accomplish this diagnosing procedure?