MBE 900 DDEC VI Troubleshooting – Section 100.3 SPN 2798/FMI 5

Section 100.3
SPN 2798/FMI 5

This diagnosis is typically injector unit pump control valve cylinders #4, 5, or 6 circuit is shorted to battery/power.‪

Section 100.3.1
Short to Battery/Power Check

Check as follows:‪

1. Turn the ignition OFF.
2. Disconnect the MCM 120–pin connector.
3. Using the J-48475 breakout box and appropriate overlay, connect the MCM side of the harness ONLY.
4. Turn the ignition ON (key ON, engine OFF).
5. Measure the voltage between pin 5 of the J-48475 breakout box and ground.
   1. If voltage is greater than 0.5 V, contact the Detroit Diesel Customer Support Center at 313–592–5800 for authorization to replace the MCM..
   2. If no voltage is present, go to the next step.
6. Turn the ignition OFF.
7. Connect the Engine Harness side of the J-48475 breakout box.
8. Turn the ignition ON (key ON, engine OFF).
9. Disconnect the #4 unit pump.
10. Measure the voltage between pin 4 of the MCM 120–pin connector and ground.
    1. If voltage is present, repair the short circuit to power between pin 4 of the MCM 120–pin connector and the #1 unit pump. See Figure "Unit Pumps #4, 5, and 6" . Refer to "100.4.1.1 Verify Repairs" .
    2. If no voltage is present, go to the next step.
    

    Figure 1. Unit Pumps #4, 5, and 6

11. Disconnect the #5 unit pump.
12. Measure the voltage between pin 8 of the MCM 120–pin connector and ground.
    1. If voltage is present, repair the short circuit to power between pin 8 of the MCM 120–pin connector and the #5 unit pump. See Figure "Unit Pumps #4, 5, and 6" . Refer to "100.4.1.1 Verify Repairs" .
    2. If no voltage is present, go to the next step.
13. Disconnect the #6 unit pump.
14. Measure the voltage between pin 6 of the MCM 120–pin connector and ground.
    1. If voltage is present, repair the short circuit to power between pin 6 of the MCM 120–pin connector and the #6 unit pump. See Figure "Unit Pumps #4, 5, and 6" . Refer to "100.4.1.1 Verify Repairs" .
    2. If no voltage is present, repair the short circuit to power between 11, 13 and/or 15 of the MCM 120–pin connector and unit pumps #4, 5, or 6. See Figure "Unit Pumps #4, 5, and 6" . Refer to "100.4.1.1 Verify Repairs" .