MBE 900 – Section 2.5 DDEC-ECU (Engine Control Unit)

Section 2.5
DDEC-ECU (Engine Control Unit)

The DDEC-ECU or engine-resident control unit is located on the left-hand side of the engine. See Figure "DDEC-ECU Control Unit Location" . The DDEC-ECU is connected by a proprietary datalink to the vehicle control unit (DDEC-VCU). All necessary data and information is exchanged through the datalink. The DDEC-VCU then broadcasts all information on the J1587 and J1939 data links, where it can be read by minidiag2.‪

The DDEC-ECU processes the data received from the DDEC-VCU, for example the position of the accelerator pedal, engine brake, etc.‪

These data are evaluated together with the data from the sensors on the engine, such as:‪

• Intake manifold pressure and temperature
• Coolant temperature
• Fuel temperature
• Oil pressure

The data is then compared to the characteristic maps or lines stored in the DDEC-ECU.‪

From these data, quantity and timing of injection are calculated and the unit pumps are actuated accordingly through the solenoid valves.‪

Figure 1. DDEC-ECU Control Unit Location

Note: To obtain a replacement DDEC-ECU control unit, all the data given on the DDEC-ECU control unit data plate is required. The data plate is located on the face of the DDEC-ECU unit. See Figure "Control Unit Data Plate" .

Figure 2. Control Unit Data Plate

Section 2.5.1
DDEC-ECU Control Unit Removal

Remove the DDEC-ECU as follows:‪

1. Open the hood.
2. Disconnect the oil level sensor wiring from the DDEC-ECU control unit by removing the bolt holding it in place.
3. Pull up on the locking bar on the vehicle wiring harness connector and disconnect it from the DDEC-ECU unit. See Figure "DDEC-ECU Control Unit Removal" .
   

   1. Engine Trim Panel‪	5. Locking Bar‪
   2. Spacer‪	6. Vehicle Wiring Harness‪
   3. Rubber Damper‪	7. Engine Wiring Harness‪
   4. Hex bolt‪

   Figure 3. DDEC-ECU Control Unit Removal

4. Rotate the locking bar on the engine wiring harness connector and disconnect it from the DDEC-ECU unit.
5. Remove the four hex bolts and rubber dampers holding the DDEC-ECU control unit to the engine. Then remove the unit.

   Note: Do not disassemble the DDEC-ECU control unit. It cannot be serviced.

Section 2.5.2
DDEC-ECU Installation

Install the DDEC-ECU as follows:‪

1. Using the four spacers and hex bolts, and eight rubber dampers, attach the DDEC-ECU control unit to the engine. Make sure the rubber dampers are installed correctly, with the flanged ends outboard. See Figure "DDEC-ECU Control Unit Installation" .
   

   1. Engine Trim Panel‪	4. Hex bolt‪
   2. Spacer‪	5. Vehicle Wiring Harness‪
   3. Rubber Damper‪	6. Engine Wiring Harness‪

   Figure 4. DDEC-ECU Control Unit Installation

2. Tighten the hex bolts 15 N·m (11 lb·ft).
3. Connect the engine wiring harness and the vehicle wiring harness to the DDEC-ECU. Lock them in place.
4. If a new DDEC-ECU control unit was installed, transfer the new dataset to it, using the applicable diagnostic tool.
5. Close the hood. Then check for normal operation.