MBE 900 DDEC VI Troubleshooting – Section 34.1 SPN 174/FMI 3

Section 34.1
SPN 174/FMI 3

SPN 174/FMI 3 indicates an Supply Fuel Temperature Sensor (SFT Sensor) open circuit.‪

Section 34.1.1
Open Circuit Check

Check as follows:‪

1. Check for multiple codes.
   1. If faults 174/3 and 110/3 are active at the same time, repair the open circuit between pin 55 of the 120–pin MCM Connector and pin 1 of the Engine Oil Temperature (EOT) Sensor and the Supply Fuel Temperature (SFT) Sensor. Refer to "34.1.1.1 Verify Repairs" .
   2. If only fault 174/3 is active, go to step 2 .
2. Disconnect the Supply Fuel Temperature Sensor.
3. Measure the resistance across pins 1 and 2 of the SFT Sensor. See Figure "Supply Fuel Temperature Sensor" .
   

   Figure 1. Supply Fuel Temperature Sensor

   1. If the resistance is greater than 4k Ω, replace SFT Sensor. Refer to "34.1.1.1 Verify Repairs" .
   2. If the resistance is less than 4k Ω, go to step 4 .
4. Turn the ignition ON (key ON, engine OFF).
5. Measure the voltage between pins 1 and 2 of the SFT Sensor harness connector.
   1. If the voltage is between 2.75 and 3.25 volts, go to step 7 .
   2. If the voltage is less than 2.75 volts, go to step 6 .
6. Measure the voltage between pin 2 of the SFT Sensor harness connector and ground.
   1. If the voltage is between 2.75 and 3.25 volts, repair the open circuit between pin 1 of the SFT Sensor harness connector and pin 55 of the 120–pin MCM connector.See Figure "MCM 120–pin Connector" . Refer to "34.1.1.1 Verify Repairs" .
   2. If the voltage is less than 2.75 volts, repair the open circuit between pin 2 of the SFT Sensor harness connector and pin 77 of the 120–pin MCM connector. See Figure "MCM 120–pin Connector" . Refer to "34.1.1.1 Verify Repairs" .
   

   Figure 2. MCM 120–pin Connector

7. Disconnect the 120–pin MCM connector and measure the resistance between pins 1 and 2 of the SFT Sensor harness connector.
   1. If the resistance is less than 5 Ω, repair the short between pins 55 and 77 of the 120–pin MCM connector. Refer to "34.1.1.1 Verify Repairs" .
   2. If the resistance is greater than 5 Ω, replace the sensor. Refer to "34.1.1.1 Verify Repairs" .

Section 34.1.1.1
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.