Pinpoint Test A: No Communication With The Vehicle Security Module

A1 CHECK THE VOLTAGE TO THE VEHICLE SECURITY MODULE
- Key in OFF position.
- Disconnect: Vehicle Security Module C203a.
- Disconnect: Vehicle Security Module C203b.
- Key in ON position.
- Measure the voltage between the vehicle security module C203a-12, circuit 517 (BK/WH), harness side and ground; and between the vehicle security module C203b-25, circuit 640 (RD/YE), harness side and ground.
  
  Fig 1: Measuring Voltage Between Vehicle Security Module C203A-12 (BK/WH), Vehicle Security Module C203B-25 (RD/YE), Harness Sides & Ground
  Courtesy of FORD MOTOR CO.
- Are the voltages greater than 10 volts?
Yes : GO to A2 .

No : VERIFY the central junction box (CJB) fuse 2 (10A) and 23 (20A) are OK. If OK, REPAIR the circuit(s) in question. CLEAR the DTCs. REPEAT the self-test.
A2 CHECK THE GROUND CIRCUITS FOR AN OPEN
- Key in OFF position.
- Measure the resistance between the vehicle security module C203a-13, circuit 1205 (BK), harness side and ground; and between the vehicle security module C203b-14, circuit 57 (BK), harness side and ground.
  
  Fig 2: Measuring Resistance Between Vehicle Security Module C203A-13 (BK), Vehicle Security Module C203B-14 (BK), Harness Sides & Ground
  Courtesy of FORD MOTOR CO.
- Are the resistances less than 5 ohms?
Yes : REFER to MODULE COMMUNICATIONS NETWORK to continue communication diagnostics.

No : REPAIR the circuit(s) in question. CLEAR the DTCs. REPEAT the self-test.