John Deere 002172.09 – CCU or ECU/VCU: CAN BUS Message Fault SCV 12, Front Chassis Module (SCO)

A communication error has occurred on the CAN bus, indicating that the main vehicle control unit has lost connection with the Secondary Hydraulic Control Unit (SCO) at source address 172. The SCO, also known as the Front Chassis Module, manages the Selective Control Valves (SCVs). When this fault is active, messages from the SCO are not received, resulting in a loss of function for the affected SCV circuits.

• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 8120
• 8220
• 8320
• 8420
• 8520
• 9230
• 9330
• 9420
• 9430
• 9530
• 9630

1. 1

   Check for other active or stored fault codes that may indicate a broader CAN bus or power supply issue.

2. 2

   Perform a cold boot by turning the key switch OFF for at least 60 seconds, then restart the machine to see if the communication fault clears.

3. 3

   Perform a CAN bus resistance check at the 9-pin diagnostic connector (Pins C and D) with the battery disconnected. The expected reading is approximately 60 Ohms.

4. 4

   Perform a CAN bus voltage check with the key ON and engine OFF. Pin C (CAN High) should be 2.5V to 3.5V, and Pin D (CAN Low) should be 1.5V to 2.5V.

5. 5

   Visually inspect the wiring harness leading to the SCV stack and the Front Chassis Module (SCO) for chafing, pinching, or corrosion.

6. 6

   Inspect the SCO module connectors for corrosion, pushed-out pins, or loose connections.

1. 1

   Isolate the fault

   If the initial CAN bus resistance check shows 120 Ohms, unplug controllers one by one until the resistance returns to 60 Ohms to isolate the open circuit.

2. 2

   Disconnect SCO module

   Locate the Secondary Hydraulic Control Unit (SCO) on the tractor frame and disconnect its main electrical connector.

3. 3

   Re-check CAN resistance

   With the SCO module disconnected, repeat the resistance measurement at the diagnostic port. If it reads 120 Ohms, the SCO module or its internal resistor is faulty. If it remains unchanged, the fault is in the main CAN harness.

4. 4

   Inspect and test harness

   Inspect the pins on the SCO controller and harness connector for damage. Test for continuity on the CAN High and CAN Low wires between the SCO connector and the diagnostic port to rule out a wire break.

5. 5

   Replace SCO controller

   If diagnostic tests point to an internal failure of the SCO module and the wiring is confirmed good, replace the controller.

6. 6

   Program and calibrate

   Have an authorized dealer program the new controller using Service ADVISOR software and perform an SCV calibration procedure.