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My first thought was to check the OBD-2 connector power supply, but you indicate that it has power, so I will assume that it has power (though if you need to double check that, be sure it has power. It seems that most cases like this are the result of no power to the connector like when the fuse blows (I think it's the cigarette ligther fuse that feeds power to the OBD2 connector)).

Are the connector grounds good?
 

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I'm sure it could be a problem with the PCM. Diagnosis is about sorting through the possible causes to find the real cause. Unfortunately I have no experience diagnosing this problem beyond checki9ng for power to the data link connector. If you can find a good wiring diagram, it might be worth the effort to make sure all the connections/wiring between the OBD-2 connector and the PCM are intact.
 
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