34.1 SPN 174/FMI 3
SPN 174/FMI 3 indicates a SFT Sensor open circuit or short to power.
34.1.1
Open Circuit/Short to Power Check
Check as follows:
1. Turn the ignition ON (key ON, engine OFF).
2. Check for multiple codes.
[a] If codes 110/3, 174/3, 175/3 and 3510/3 are active at the same time, go to step 3.
[b] If only fault 174/3 is active, go to step 5.
3. Disconnect the Supply Fuel Temperature Sensor (ECT Sensor).
4. Measure the voltage between pin 1 of the SFT Sensor and ground.
[a] If the voltage is greater than 2.75 volts, repair the short to power between pin 55 of
the MCM 120–pin connector and the Engine Coolant Temperature Sensor, the Engine
Oil Temperature Sensor and the Supply Fuel Temperature Sensor. Refer to section
34.1.1.1.
[b] If no voltage is present on pin 1 of the SFT Sensor, repair the open between pin 55 of
the MCM 120–pin connector and the Engine Coolant Temperature Sensor, the Engine
Oil Temperature Sensor and the Supply Fuel Temperature Sensor. Refer to section
34.1.1.1.
5. Disconnect the SFT Sensor.
6. Measure the resistance across pins 1 and 2 of the SFT Sensor. See Figure 34-1.
[a] If the resistance is greater than 4k Ω, replace SFT Sensor. Refer to section 34.1.1.1.
[b] If the resistance is less than 4k Ω, go to step 7.
7. Turn the ignition ON (key ON, engine OFF).
8. Measure the voltage between pins 1 and 2 of the SFT Sensor harness connector.
[a] If the voltage is between 2.75 and 3.25 volts, refer to section 34.1.1.1.
[b] If the voltage is less than 2.75 volts, go to step 9.
9. Measure the voltage between pin 2 of the SFT Sensor harness connector and ground.
[a] 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 34-2. Refer to section 34.1.1.1.
[b] 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
34-2. Refer to section 34.1.1.1.
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.
34.2 SPN 174/FMI 4
SPN 174/FMI 4 indicates a SFT Sensor short to ground.
34.2.1
Short to Ground Check
Check as follows:
1. Disconnect the SFT Sensor.
2. Disconnect the 120-pin MCM connector.
3. Measure the resistance across pins 1 and 2 of the SFT Sensor connector.
[a] If resistance is less than 5 Ω, repair short between wires 55 and 77 of the 120-pin
MCM connector. Refer to section 34.2.1.1.
[b] If resistance is greater than 5 Ω, go to step 4.
4. Measure the resistance between pin 2 of the SFT Sensor harness connector and ground.
[a] If resistance is less than 5 Ω, repair the short circuit between pin 2 of the SFT Sensor
harness connector and ground. Refer to section 34.2.1.1.
[b] If resistance is greater than 5 Ω, review steps 3 through 4. If the results are the same,
contact Detroit Diesel Customer Support Center (313–592–5800).
34.2.1.1
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.
