New Holland 3946 – Engine Control Module (ECM / EDC): Continuous negative torque control demand from Driveline Retarder exceeding the maximum time.

This code indicates a CAN bus communication timeout or error. The Engine Control Module (ECM) is receiving a continuous negative torque demand signal from the Driveline Retarder controller that has exceeded the maximum allowable time limit. This is typically caused by a defect in the Driveline Retarder controller itself or a physical problem with the CAN cable connecting the retarder to the engine network.

• Heavy-duty tractors
• Wheel loaders
• Backhoe loaders
• B90B
• B100B
• B110B
• B115B

1. 1

   Connect a diagnostic tool to retrieve the active DTC 3946 and check for any accompanying CAN bus timeout codes.

2. 2

   Visually inspect the CAN cable connecting the Driveline Retarder controller to the Engine ECM for chafing, pinched wires, or disconnected plugs.

3. 3

   With the battery disconnected, measure the resistance across the CAN High and CAN Low pins (should read around 60 ohms if network resistors are intact) and check for short circuits to ground or power.

4. 4

   Verify that the Driveline Retarder controller is receiving proper operating voltage and has a clean ground connection, as under-voltage can cause the controller to drop off the CAN network.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery terminal to prevent electrical shorts during testing.

2. 2

   Access the Modules

   Locate the Driveline Retarder controller and the Engine ECM on your specific machine.

3. 3

   Harness Testing

   Disconnect the CAN harness at both the retarder controller and the ECM. Use a multimeter to perform a continuity test on the CAN lines.

4. 4

   Repair Wiring

   If an open circuit, high resistance, or short circuit is found in the wiring, repair the damaged section of the harness or replace the CAN cable entirely.

5. 5

   Replace the Controller

   If the CAN wiring, power, and ground to the Driveline Retarder controller all test perfectly, the internal CAN controller of the Driveline Retarder unit is defective. Remove the mounting hardware, disconnect the module, and install a replacement OEM controller.

6. 6

   Reassemble and Clear Codes

   Reconnect all harnesses and the battery. Connect your diagnostic tool, clear the 3946 fault code, and perform a test drive (utilizing the retarder) to ensure the code does not return.