Ford PWM J1850, hardware limits
I've been fighting our dead 2001 Windstar. It died on the road with no communication to the DLC connector.
I sent the PCM in for repair, I got it back and still can't connect to my Actron scanner and the Ford is still dead. The scanner worked fine with the Ford before the problem and it works fine with the old Saab 9000 setting right next to the Ford. I'm beginning to wonder if the problem is on the SCP buss on the vehicle. I tested all populated circuits between the PCM connector and the vehicle with an ohmmeter, the only strange things I noticed are:
SCP Data+ = 120 ohms to ground
SCP Data- = 0.6 Megohms to ground
..and Data+ to Data- = 1250 K ohm
I would have expected less resistance between Data+ and Data-.
Is the 120 ohms to ground too much load?