Pinpoint Test G: No Communication With The Electronic Automatic Temperature Control Module

G1 CHECK CIRCUIT 875 (BK/LB) FOR AN OPEN
- Key in OFF position.
- Disconnect: EATC Module C228a.
- Measure the resistance between EATC module C228a-2, circuit 875 (BK/LB) and ground.
  
  Fig 1: Checking Circuit 875 (BK/LB) For Open
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 25 ohms?
Yes: GO to G2.

No: REPAIR circuit 875 (BK/LB) for an open. TEST the system for normal operation.
G2 CHECK CIRCUIT 729 (RD/WH) FOR B+
- Disconnect: EATC module C228b.
- Measure the voltage between EATC module C228a-3, circuit 729 (RD/WH) and ground.
  
  Fig 2: Checking Circuit 729 (RD/WH) For B+
  Courtesy of FORD MOTOR CO.
- Is the voltage B+?
Yes: GO to G3.

No: VERIFY the central junction box (CJB) fuse 5 (7.5A) is OK. If OK, REPAIR circuit 729 (RD/WH) for an open. TEST the system for normal operation.
G3 CHECK CIRCUIT 296 (WH/VT) FOR B+
- Key in ON position.
- Measure the voltage between EATC module C228a-16, circuit 296 (WH/VT) and ground.
  
  Fig 3: Checking Circuit 296 (WH/VT) For B+
  Courtesy of FORD MOTOR CO.
- Is the voltage B+?
Yes: REFER to MODULE COMMUNICATIONS NETWORK to diagnose a network concern.

No: VERIFY the central junction box (CJB) fuse 13 (10A) is OK. If OK, REPAIR circuit 296 (WH/VT) for an open. TEST the system for normal operation.