MBE 900 DDEC VI Troubleshooting – Section 100.2 SPN 2798/FMI 4

Section 100.2
SPN 2798/FMI 4

This diagnosis is typically injector control valve cylinder #4, 5, or 6 circuit is shorted to ground.‪

Section 100.2.1
Short to Ground Check

Check as follows:‪

1. Disconnect the MCM 120–pin connector and connect the J-48475 breakout box and appropriate overlay. Connect ONLY the Engine Harness side cable. DO NOT connect the MCM side.
2. Measure the resistance between pin 16 of the MCM 120–pin connector and ground.
   1. If the resistance is greater than 3 Ω, go to step 8 .
   2. If the resistance is less than 3 Ω, go to the next step.
3. Disconnect the 12–pin injector valve cover harness connector.
4. Measure the resistance between pin 7 on the valve cover side of the injector harness connector and ground. If you are using the injector breakout box (J-48475 ), use pin 1 of injector #4.
   1. If the resistance is greater than 3 Ω, repair the short to ground between pins 16 or 17 of the MCM 120–pin connector and pins 7 and 8 on the engine side of the injector harness connector. See Figure "Injectors #4, 5, 6" . Refer to "100.4.1.1 Verify Repairs" .
      

      Figure 1. Injectors #4, 5, 6

   2. If the resistance is less than 3 Ω, go to the next step.
5. Remove the cylinder #4 valve cover.
6. Disconnect the injector #4 connector.
7. Measure the resistance between either stud of injector #4 and ground.
   1. If the resistance is less than 3 Ω, replace the injector. Refer to "100.4.1.1 Verify Repairs" .
   2. If the resistance is greater than 3 Ω, replace the under valve cover injector harness. Refer to "100.4.1.1 Verify Repairs" .
8. Measure the resistance between pin 20 of the MCM 120–pin connector and ground.
   1. If the resistance is less than 3 Ω, go to step 14 .
   2. If the resistance is greater than 3 Ω, go to the next step.
9. Disconnect the 12–pin injector valve cover harness connector.
10. Measure the resistance between pin 9 on the valve cover side of the injector harness connector and ground. If you are using the injector breakout box (J-48475 ), use pin 1 of injector #5.
    1. If the resistance is greater than 3 Ω, repair the short to ground between pins 20 or 21 of the MCM 120–pin connector and pins 9 and 10 of the engine side of the injector harness connector. Refer to "100.4.1.1 Verify Repairs" .
    2. If the resistance is less than 3 Ω, go to the next step.
11. Remove the cylinder #5 valve cover.
12. Disconnect the injector #5 connector.
13. Measure the resistance between either injector #5 connector stud and ground.
    1. If the resistance is less than 3 Ω, replace the injector. Refer to "100.4.1.1 Verify Repairs" .
    2. If the resistance is greater than 3 Ω, replace the under valve cover injector harness. Refer to "100.4.1.1 Verify Repairs" .
14. Measure the resistance between pin 18 of the MCM 120–pin connector and ground.
    1. If the resistance is less than 3 Ω, go to the next step.
    2. If the resistance is greater than 3 Ω, contact the Detroit Diesel Customer Support Center at 313–592–5800 for authorization to replace the MCM.
15. Disconnect the 12–pin injector valve cover harness connector.
16. Measure the resistance between pin 11 on the valve cover side of the injector harness connector and ground. If you are using the injector breakout box (J-48475 ), use pin 1 of injector #6.
    1. If the resistance is less than 3 Ω, go to the next step.
    2. If the resistance is greater than 3 Ω, repair the short circuit to ground between pins 18 or 19 of the MCM 120–pin connector and pins 11 and 12 on the engine side of the injector harness connector. See Figure "Injectors #4, 5, 6" . Refer to "100.4.1.1 Verify Repairs" .
17. Remove the cylinder #6 valve cover.
18. Disconnect the #6 injector connector.
19. Measure the resistance between either injector connector stud and ground.
    1. If the resistance is less than 3 Ω, replace the injector. Refer to "100.4.1.1 Verify Repairs" .
    2. If the resistance is greater than 3 Ω, replace the under valve cover injector harness. Refer to "100.4.1.1 Verify Repairs" .