New Holland ENG 3320 – Engine ECU (EDC - Electronic Diesel Control): DM1DCU SPN3 message - Error in DCU active

This is a CAN bus communication code indicating that the Engine Control Unit (ECU) is receiving a DM1 (Diagnostic Message 1) from the Dosing Control Unit (DCU) indicating that the DCU has an active internal fault.

• T7 Series (Tier 4B)
• T8.xxx Series
• T9 Series
• T9.615
• CR9090
• CX8080 Elevation
• CX8090 Elevation

1. 1

   Read DCU Codes: Connect the CNH Electronic Service Tool (EST) to read the specific internal fault codes stored directly in the DCU (e.g., low DEF pressure, temperature sensor faults, or internal memory errors).

2. 2

   Check DEF Fluid: Verify that the AdBlue/DEF tank is not empty and that the fluid is not contaminated or degraded.

3. 3

   Inspect Wiring & CAN Bus: Check the wiring harness, specifically the CAN bus communication lines (CAN A/B/C) between the Engine ECU and the DCU. Look for chafed wires, corrosion, or bent pins at the connectors.

4. 4

   Verify Power/Ground: Ensure the DCU is receiving proper voltage and has a clean ground connection.

5. 5

   Inspect DEF Lines: Check for blocked, frozen, or leaking DEF lines, which can cause the DCU to register a critical system failure.

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical spikes.

2. 2

   Locate the DCU

   Locate the DENOX Dosing Control Unit (typically mounted near the DEF tank or SCR catalyst assembly).

3. 3

   Disconnect

   Carefully unplug the multi-pin electrical harness connector from the DCU.

4. 4

   Remove

   Unbolt the mounting hardware securing the DCU to the bracket and remove the module.

5. 5

   Install

   Mount the replacement DCU and reconnect the electrical harness.

6. 6

   Program the Module

   Connect the CNH EST diagnostic tool and flash the module with the correct machine software. (Note: CNH requires troubleshooting to be performed before they will issue programming passwords via ASIST).

7. 7

   Test

   Clear all inactive fault codes in both the Engine ECU and the DCU. Run an SCR dosing system test via the diagnostic tool to verify proper DEF injection and system operation.