New Holland ENG 3321 – Engine Control Module (ECM): Timeout of CAN Message DM1DCU SPN4

The Engine Control Module (ECM) has lost communication with the Dosing Control Unit (DCU) over the CAN bus network. The ECM expects to receive a regular diagnostic message (DM1) from the DCU, which manages the Selective Catalytic Reduction (SCR) / DEF / AdBlue system. When this message is not received within the expected timeframe, the timeout fault is triggered, which can lead to engine warning lights, power reduction (derate), and decreased fuel efficiency.

• T7 Series (T7.185, T7.260, T7.270)
• T8.xxx Series
• CR Series (CR960, CR9060)

1. 1

   Check DCU power and ground by inspecting the fuses and relays supplying power to the Dosing Control Unit

2. 2

   Inspect CAN bus wiring harness between the Engine ECM and the DCU for open circuits, short circuits, or physical damage

3. 3

   Scan CAN nodes using a diagnostic tool to see if the DCU node can be detected or shows as 'not supported'

4. 4

   Check for related CAN timeout codes (e.g., SCR1, NOx sensor timeouts) which might indicate a broader CAN bus failure rather than an isolated DCU issue

1. 1

   Disconnect the Battery

   Always disconnect the battery before performing electrical resistance checks.

2. 2

   Inspect Connectors

   Locate the Dosing Control Unit (integrated into the Denox supply module). Disconnect the DCU plug and inspect for pushed-out pins, moisture, or corrosion. Clean and repair as necessary.

3. 3

   Measure CAN Resistance

   Measure the resistance across CAN High and CAN Low at the DCU connector. A healthy CAN bus should read approximately 60 ohms with the battery disconnected.

4. 4

   Verify Voltage

   Reconnect the battery and turn the key to the ON position. Verify that the DCU is receiving proper operating voltage and has a solid ground.

5. 5

   Replace the DCU

   If the wiring, power, and ground are all verified as good, but the DCU still fails to communicate on the CAN bus, the DCU itself has failed and must be replaced.

6. 6

   Software Calibration

   If the DCU is replaced, the new module will require software installation and calibration using the CNH Electronic Service Tool (EST) to clear the fault and resume normal SCR operation.