MBE 4000 DDEC VI Troubleshooting – Section 75.1 SPN 729/FMI 3

Section 75.1
SPN 729/FMI 3

This diagnosis is typically a short to power/open.‪

Section 75.1.1
Short to Power/Open Check

Check as follows:‪

1. Disconnect the Grid Heater connector.
2. Turn the ignition ON (key ON, engine OFF).
3. Measure the voltage between pins 2 and 4 of the Grid Heater connector. See Figure "Grid Heater Wiring" .
   

   Figure 1. Grid Heater Wiring

   1. If the voltage is greater than 11.5 volts, go to step 5 .
   2. If the voltage is less than 11.5 volts, go to step 4 .
4. Measure the voltage between pin 2 of the Grid Heater connector and ground.
   1. If the voltage is greater than 11.5 volts, repair the open between pin 4 of the Grid Heater connector and pin 95 of the 120–pin MCM connector. Refer to "75.1.1.1 Verify Repairs" .
   2. If the voltage is less than 11.5 volts, repair the open between pin 2 of the Grid Heater connector and pin 41 of the 120–pin MCM connector. Refer to "75.1.1.1 Verify Repairs" .
5. Turn the ignition OFF.
6. Disconnect the 120–pin MCM connector.
7. Measure the resistance between pins 2 and 3 of the Grid Heater connector.
   1. If the resistance is greater than 5 Ω, go to step 8 .
   2. If the resistance is less than 5 Ω, repair the short between Grid Heater pins 2 and 3 and pins 41 and 92 of the 120–pin MCM connector. Refer to "75.1.1.1 Verify Repairs" .
8. Measure the resistance between pin 3 of the Grid Heater connector and pin 92 of the 120–pin MCM connector.
   1. If the resistance is greater than 5 Ω, repair the open between pin 3 of the Grid Heater connector and pin 92 of the 120–pin MCM connector. Refer to "75.1.1.1 Verify Repairs" .
   2. If the resistance is less than 5 Ω, replace the Grid Heater.

Section 75.1.1.1
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.