Rodeo Isuzu Power lock module problems..........

The locks on the driver side door are not actuating properly, I checked the power lock module and found:
is getting the right voltage
the little motor inside works
the gears are good
The motor is only getting voltage to "kick" the lock and then looses power therefore not engaging the lock fully. I found there is only voltage going to the motor half way thru the full rotation of the main gear.....What should I check???? This thing is 140.00 dollars brand new....too much. What are the two diodes inside for???? I will appreciate any assistance..
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