John Deere 2003.19 – Engine Control Unit (ECU) / Monitor Display Unit (MDU) / Chassis Control Unit (CCU): Communication Error with Source Address 3 / Loss of TCU CAN Messages

The main controller has stopped receiving expected CAN bus messages from the transmission or vehicle controller (TCU/VCU). On some equipment, this is also described as a 'Flexpower Counter' error or 'CAN communication error; engine control unit (ECU) has lost communication with VCU'.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5090M
• 5115M
• 250D
• 300D
• 350D
• 400D
• 310SK
• 410K
• 210K
• 3029 Diesel Engine
• 4.5L PowerTech engine
• 6.8L PowerTech engine
• 9.0L PowerTech engine

1. 1

   Check for other active codes: Check the monitor for any active TCU or VCU codes (e.g., low voltage). If the TCU/VCU is broadcasting its own internal fault codes, diagnose and clear those first.

2. 2

   Check power and ground to the TCU/VCU: Check the unswitched and switched power fuses for the TCU/VCU (e.g., 10-Amp TCU fuses). A module that loses power cannot broadcast on the CAN bus.

3. 3

   Perform a CAN Bus Resistance Test: With the machine powered off and the battery disconnected, measure the resistance across the CAN High and CAN Low pins at the diagnostic connector. It should read approximately 60 ohms. A reading of 120 ohms indicates a failed terminating resistor or open circuit.

4. 4

   Inspect the wiring harness: Check the connectors at the ECU, CCU, and TCU/VCU for corrosion, moisture, or pushed-back pins.

1. 1

   Clear Codes and Test

   Clear the active diagnostic trouble codes and operate the machine on a smooth, level surface through all gear ranges to see if the code returns.

2. 2

   Inspect and Clean Connectors

   Disconnect the main harness connectors at the TCU/VCU and the ECU. Spray with electrical contact cleaner, ensure no pins are bent, and apply dielectric grease before reconnecting.

3. 3

   Replace Blown Fuses

   If the TCU/VCU power fuses are blown, replace them. If they blow immediately upon key-on, trace the power wire for a short to ground.

4. 4

   Repair CAN Wiring

   If the CAN bus resistance test fails, trace the yellow and green CAN wires between the ECU and TCU. Repair any chafed, broken, or melted wires.

5. 5

   Replace Terminating Resistor

   If the wiring is intact but resistance is incorrect, locate and replace the faulty 120-Ohm CAN Termination Node.

6. 6

   Replace/Reprogram the TCU/VCU

   If power, ground, and CAN wiring all test perfectly at the TCU/VCU connector, the module itself has failed internally and must be replaced and reprogrammed by a dealer.