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.‪

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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" .

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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" .
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     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" .
    Click to see this graphic in a separate window

     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.


MBE 900 Service Manual - 6SE414
Generated on 10-13-2008