Pinpoint Test D: No Communication With The 4WD Control Module (Gem)

WARNING: This page is about a different car, the 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

D1 CHECK CIRCUITS 1002 (BK/PK), 640 (RD/YE) AND 33a (WH/PK) FOR VOLTAGE
- Key in OFF position.
- Disconnect: 4WD Control Module (GEM) C281a.
- Disconnect: 4WD Control Module (GEM) C281b.
- Key in ON position.
- Measure the voltage between 4WD control module C281a, pin 5, circuit 640 (RD/YE) and ground; and between 4WD control module C281a, pin 6, circuit 1002 (BK/PK) and ground.
  
  Fig 1: Measuring Voltage Between C281A, Pin 5 And Ground; And Between C281A, Pin 6 And Ground
  Courtesy of FORD MOTOR CO.
- Measure the voltage between 4WD control module C281b, pin 8, circuit 33a (WH/PK) (pick-up only) and ground.
  
  Fig 2: Measuring Voltage Between C281B, Pin 8 And Ground
  Courtesy of FORD MOTOR CO.
- Are the voltages greater than 10 volts?
- Yes : GO to D2.
- No : REPAIR the circuits as necessary. TEST the system for normal operation.
D2 CHECK CIRCUIT 57 (BK) FOR AN 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.