New Holland DCU 19678 – DCU (Dosing Control Unit): Ambient Temperature: SAE J1939 Check for CAN receive signal

The Dosing Control Unit (DCU) is receiving an erratic, out-of-range, or unavailable signal regarding the ambient air temperature over the SAE J1939 CAN bus network. Specifically, the system is flagging 'too many CAN messages' or a timeout/erroneous signal, which triggers the OBD2 equivalent code P0071.

• New Holland T7 Series (T7.220, T7.235, T7.250, T7.260, T7.270)
• New Holland T8 Series

1. 1

   Check CAN bus wiring harness and connectors between the Engine Control Module (ECM), the DCU, and the sensor for chafing, corrosion, or loose pins

2. 2

   Inspect the Ambient Air Temperature Sensor pigtail connector for moisture, dirt, or bent pins

3. 3

   Use an electronic service tool (EST) to monitor the Ambient Air Temperature value and compare it to the actual outside temperature

4. 4

   Check for related codes like DCU 19677 (timeout) or Engine codes 3517/3518 to isolate the sensor from a network-wide CAN issue

1. 1

   Disconnect Battery

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

2. 2

   Clean and Re-seat Connectors

   Disconnect the harness at the Ambient Air Temperature Sensor and the DCU. Spray with electrical contact cleaner, ensure pins are straight, and firmly reconnect them.

3. 3

   Test the Harness

   If the connectors are clean, use a multimeter to check for continuity and ensure there are no shorts to ground or power on the sensor signal and return wires.

4. 4

   Replace the Sensor

   If the wiring is intact and the CAN bus is functioning normally but the sensor still reads out of range, replace the Ambient Air Temperature Sensor.

5. 5

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use the diagnostic service tool to clear the DCU 19678 and P0071 fault codes.

6. 6

   Verify Repair

   Start the engine and monitor the ambient temperature reading on the dash or service tool to ensure it remains stable and accurate.