Section 120.1
SPN 3661/FMI 14

This diagnosis is typically an open circuit, short to ground or short to power.‪

Section 120.1.1
Open Circuit, Short to Ground or Short to Power Check

Check as follows:‪

1. Check for multiple codes.
   1. If fault code 168/1 is active , service 168/1 first. Refer to "32.2 SPN 168/FMI 1" .
   2. If fault 3659/14 and 3660/14 are active in addition to 3661/14, go to step 2 .
   3. If only fault code 3661/14 is active, go to step 10 .
2. Turn the ignition OFF.
3. Disconnect the Front Injector Harness 12–pin connector.
4. Inspect the Front Injector Harness 12–pin connector for bent or spread pins, inspect the connector seal for damage (signs of water or oil intrusion).
   1. If the water or oil intrusion, bent or spread pins are found, repair as necessary. Refer to "120.1.1.1 Verify Repairs" .
   2. If connector shows no signs of damage, go to step 5 .
5. Measure the resistance between pins 9 and 6 on the valve cover side of the Front Injector Harness. If using J-48671–10 , measure between injector #3 pins 3 and 4.
   1. If the resistance is greater than 3 Ω, replace the under valve cover injector harness. Refer to "120.1.1.1 Verify Repairs" .
   2. If the resistance is less than 3 Ω, go to step 6 .
6. Disconnect the MCM 120–pin connector.
7. Measure the resistance between pin 11of the MCM 120–pin connector and pin 9 of the Front Injector Harness 12–pin connector.
   1. If the resistance is less than 3 Ω, go to step 8 .
   2. If the resistance is greater than 3 Ω, repair the open between pin 11 of the MCM 120–pin connector and pin 9 of the Front Injector Harness 12–pin connector. Refer to "120.1.1.1 Verify Repairs" .
8. Disconnect the negative battery cable.
9. Measure the resistance between the positive battery post and pin 11of the MCM 120–pin connector.
   1. If the resistance is greater than 3 Ω, contact the Detroit Diesel Customer Support Center at 313–592–5800 for MCM replacement authorization.
   2. If the resistance is less than 3 Ω, repair the short to power between battery positive and pin 11 of the MCM 120–pin connector. See Figure "120–pin MCM Connector" . Refer to "120.1.1.1 Verify Repairs" .
   

   Figure 1. 120–pin MCM Connector

10. Turn the ignition OFF.
11. Disconnect the Front Injector Harness 12–pin connector.
12. Measure the resistance between pin 9 and pin 6 on the valve cover side of the injector harness. If using J-48671–10 , measure between injector #3 pins 3 and 4.
    1. If the resistance is greater than 3 Ω, go to step 13 .
    2. If the resistance is less than 3 Ω, go to step 18 .
13. Remove the upper valve cover.
14. Disconnect injector #3.
15. Measure the resistance between pin 9 on the valve cover side of the Front Injector Harness and pin 3 of the injector #3 harness connector. If usingJ-48671–10 , measure between injector #3 pin 3 and the injector #3 harness connector pin 3.
    1. If the resistance is greater than 3 Ω, replace the under valve cover injector harness. Refer to "120.1.1.1 Verify Repairs" .
    2. If the resistance is less than 3 Ω, go to step 16 .
16. Measure the resistance between pin 6 on the valve cover side of the Front Injector Harness and pin 4 of the injector #3 harness connector. If using J-48671–10, measure between injector #3 pin 4 and the injector #3 harness connector pin 4.
    1. If the resistance is greater than 3 Ω, replace the under valve cover injector harness. Refer to "120.1.1.1 Verify Repairs" .
    2. If the resistance is less than 3 Ω, go to step 17 .
17. Measure the resistance between pin 4 on the valve cover side of the Front Injector Harness and ground. If using J-48671–10 , measure between injector #3 pin 4 and ground.
    1. If the resistance is greater than 3 Ω, replace injector #3. Refer to "118.1.1.1 Verify Repairs" .
    2. If the resistance is less than 3 Ω, replace the under valve cover injector harness. Refer to "120.1.1.1 Verify Repairs" .
18. Measure the resistance between pin 4 on the valve cover side of the Front Injector Harness and ground. If using J-48671–10 , measure between injector #3 pin 4 and ground.
    1. If the resistance is greater than 3 Ω, repair the short to ground between pin 12 of the 120–pin MCM connector and pin 2 of the Front Injector Harness 12–pin connector. Refer to "120.1.1.1 Verify Repairs" .
    2. If the resistance is less than 3 Ω, go to step 19 .
19. Remove the upper valve cover.
20. Disconnect the injector #3 connector.
21. Measure the resistance between pin 4 on the valve cover side of the Front Injector Harness and ground. If using J-48671–10 , measure between injector #3 pin 4 and ground.
    1. If the resistance is greater than 3 Ω, replace injector #3. Refer to "120.1.1.1 Verify Repairs" .
    2. If the resistance is less than 3 Ω, replace the under valve cover injector harness. Refer to "120.1.1.1 Verify Repairs" .

Section 120.1.1.1
Verify Repairs

Verify repairs as follows:‪

1. Turn ignition OFF.
2. Reconnect any electrical connections that were disconnected to perform the diagnosis.
3. Clear codes with DDDL 7.0 or latest version.
4. Start and bring engine up to operating temperature (over 140°F/60°C).
5. Verify operation is satisfactory and no warning lamps illuminate. If warning lamps illuminate, troubleshoot the codes. If assistance is required, call the Detroit Diesel Customer Support Center at 313–592–5800.