Pinpoint Test B: No Communication With The 4WD Control Module

B1 CHECK CIRCUITS 1002 (BK/PK), 640 (RD/YE) AND 33a (WH/PK) FOR VOLTAGE
- Key in OFF position.
- Disconnect: 4WD Control Module C281a.
- Disconnect: 4WD Control Module C281b.
- Key in ON position.
- Measure the voltage between 4WD control module C281a, pin 5, circuit 640 (RD/YE) and ground; 4WD control module C281a, pin 6, circuit 1002 (BK/PK) and ground; 4WD control module C281b, pin 8, circuit 33a (WH/PK) (pick-up only) and ground.
  
  Fig 1: Checking Circuits 1002 (BK/PK), 640 (RD/YE) And 33A (WH/PK) For Voltage (1 Of 2)
  Courtesy of FORD MOTOR CO.
  
  Fig 2: Checking Circuits 1002 (BK/PK), 640 (RD/YE) And 33A (WH/PK) For Voltage (2 Of 2)
  Courtesy of FORD MOTOR CO.
- Are the voltages greater than 10 volts?
- Yes : GO to B2.
- No : REPAIR the circuits as necessary. TEST the system for normal operation.
B2 CHECK CIRCUIT 57 (BK) FOR OPEN
- Measure the resistance between 4WD control module C281a pin 3, circuit 57 (BK), harness side and ground.
  
  Fig 3: Measuring Resistance Between 4WD Control Module C281A Pin 3, Circuit 57 (BK), Harness Side And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : CHECK the module communication network. refer to MODULE COMMUNICATIONS NETWORK .
- No : REPAIR the circuit. TEST the system for normal operation.