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Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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23,851 Posts
Check for powers and grounds at the PCM. The Rd/Wt wire should have 12 volts battery power. The Wt/Bk wire should have 12 volts with the ign on. Both Bk/Tn's need to be a good ground. With these in place, the scan tool should be able to communicate with the PCM.
The Dk.Gn/Or wire from the ASD relay is powered by fuse #3 in the underhood (PDC) fuse/relay box. It also powers the PCM and ign coil. It has power for a couple of seconds after theign is turned on and turns back off if the PCM doesn't detect engine rotation through the crank position sensor.
If the 5 volt (Vt/Wt) or 8 volt (Or) sensor wire outputs from the PCM are shorted to ground, the PCM will go into protection and not communicate either.
 

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Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
Joined
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23,851 Posts
That sounds like the problem. You will need to back-trace towards the underhood fuse/relay box (PDC) to find out where you are losing the 12 volts on the Rd/Wt and Wt/Bk wires.
Being near the battery could cause corrosion issues on the connectors and wiring underneath the PDC. Examine this area.
 

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Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
Joined
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23,851 Posts
Good work!
 
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