Pinpoint Test D: High-Speed Controller Area Network (HS-CAN) Communications Bus Fault

Refer to appropriate SYSTEM WIRING DIAGRAMS - EDGE or SYSTEM WIRING DIAGRAMS - MKX article for All Wheel Drive (AWD) schematic and connector information.

Normal Operation 

The on-demand four wheel drive (4WD) system uses data from other systems as inputs to the 4X4 control module. The 4X4 control module uses the inputs to determine the appropriate duty cycle to send to the active torque control coupling (ATCC) solenoid (part of rear axle) that delivers the desired torque to the rear wheels. Specific inputs to the 4X4 control module are: accelerator pedal position output from the PCM, transmission range from the PCM, brake system status and all 4 wheel speeds from the ABS module. Communication between the 4X4 control module and other modules is obtained through the high-speed controller area network (HS-CAN). If the 4X4 control module loses communication with, or receives invalid data from any of the necessary modules, DTCs are set and the 4X4 control module may not allow 4WD operation.

• DTC U0100 Lost Communication with ECM/PCM - When the 4X4 control module detects a missing HS-CAN bus message from the PCM for at least 5 seconds, this DTC is set.
• DTC U0121 Lost Communication with Anti-lock Brake System (ABS) Control Module - When the 4X4 control module detects a missing HS-CAN bus message from the ABS module for at least 5 seconds, this DTC is set.

This pinpoint test is intended to diagnose the following:

• 4X4 control module
• PCM
• ABS module
• Wiring, terminals or connectors

PINPOINT TEST D: HIGH-SPEED CONTROLLER AREA NETWORK (HS-CAN) COMMUNICATIONS BUS FAULT 

1. D1 CHECK HS-CAN CIRCUITS BETWEEN THE DATA LINK CONNECTOR (DLC) AND THE 4X4 CONTROL MODULE FOR AN OPEN 
   • Key in OFF position.
   Fig 1: Checking High Speed Can Circuits Between DLC And 4X4 Control Module For An Open
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between 4X4 control module C281-4, circuit VDB04 (WH/BU), harness side and DLC C251-6, circuit VDB04 (WH/BU), harness side; and between 4X4 control module C281-12, circuit VDB05 (WH), harness side and DLC C251-14, circuit VDB05 (WH), harness side.
   • Are the resistances less than 5 ohms? 
   1. YES  : Go to  D2.
   2. NO  : REPAIR the circuit(s). CLEAR the DTCs. REPEAT the self-test. CARRY OUT the Network Test.
2. D2 CHECK HS-CAN CIRCUITS FOR A SHORT TO GROUND 
   Fig 2: Checking High Speed CAN Circuits For A Short To Ground
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between 4X4 control module C281-4, circuit VDB04 (WH/BU), harness side and ground; and between 4X4 control module C281-12, circuit VDB05 (WH), harness side and ground.
   • Are the resistances greater than 5,000 ohms? 
   1. YES  : Go to  D3.
   2. NO  : REPAIR the circuit(s). CLEAR the DTCs. REPEAT the self-test. CARRY OUT the Network Test.
3. D3 CHECK RESISTANCE BETWEEN HS-CAN CIRCUITS 
   Fig 3: Checking Resistance Between High Speed CAN Circuits
   Courtesy of FORD MOTOR CO.
   NOTE: The PCM and the instrument cluster (IC) must be connected and operating correctly to obtain the correct resistance between the HS-CAN circuits.
   • Measure the resistance between 4X4 control module C281-4, circuit VDB04 (WH/BU) harness side and 4X4 control module C281-12, circuit VDB05 (WH) harness side.
   • Is the resistance 60 ohms (± 5 ohms)? 
   1. YES  : Go to  D4.
   2. NO  : REPAIR the circuit(s). CLEAR the DTCs. REPEAT the self-test. CARRY OUT the Network Test.
4. D4 CHECK FOR DTCs U0100 AND U0121 SET TOGETHER 
   • Key in ON position.
   • Carry out the 4X4 control module self-test.
   • Review the results of the 4X4 control module self-test.
   • Are DTCs U0100 and U0121 set together? 
   1. YES  : REFER to MODULE COMMUNICATIONS NETWORK article to continue diagnosis of the communications network.
   2. NO  : Go to  D5.
5. D5 CHECK FOR DTC U0100 
   • Refer to the results of the 4X4 control module self-test.
   • Is DTC U0100 set? 
   1. YES  : The PCM is not sending any data to the 4X4 control module. REFER to MODULE COMMUNICATIONS NETWORK article to for additional PCM diagnosis.
   2. NO  : Go to  D6.
6. D6 CHECK FOR DTC U0121 
   • Refer to the results of the 4X4 control module self-test.
   • Is DTC U0121 set? 
   1. YES  : The ABS module is not sending any data to the 4X4 control module. REFER to MODULE COMMUNICATIONS NETWORK article for additional ABS module diagnosis.
   2. NO  : Go to  D7.
7. D7 CHECK FOR CORRECT 4X4 CONTROL MODULE OPERATION 
   • Key in OFF position.
   • Disconnect the 4X4 control module.
   • Check the harness and component side connectors for:
     • corrosion.
     • pushed-out/bent pins.
   • Connect the 4X4 control module and make sure it seats correctly.
   • Operate the system and determine if the concern is still present.
   • Is the concern still present? 
   1. YES  : INSTALL a new 4X4 control module. REFER to 4X4 CONTROL MODULE . CLEAR the DTCs. REPEAT the self-test.
   2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.