SPN 174 - FMI 3 (Diagnostic Code: Fuel Temperature Sensor - Voltage Above Normal)
SPN 174 FMI 3
SPN174 FMI3
CID 0174 FMI 03 Fuel Temperature Open/Short to +Batt
CID 0174 FMI 03 Fuel Temperature Open/Short to +Batt
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| Figure 1.1 - Fuel Temp Sensor Open (174-3) |
MID 036 CID 0174 FMI 03
Conditions Which Generate This Code:
The Electronic Control Module (ECM) detects signal voltage that is above normal.
System Response:
The ECM will log the diagnostic code. The ECM flags fuel temperature as invalid data and a default value is used.
Possible Performance Effect:
Low Power
#Troubleshooting:
The troubleshooting procedures for the diagnostic codes of each temperature sensor are identical. The temperature sensors are passive sensors that have two terminals. The temperature sensors do not require supply voltage from the Electronic Control Module (ECM).
Test Step 1. Inspect Electrical Connectors and Wiring
A. Turn the keyswitch to the OFF position.
B. Thoroughly inspect ECM connectors and the connector for Fuel Temperature Sensor.
C. Perform a 45 N (10 lb) pull test on each of the wires in the sensor connector and the ECM connector
that are associated with the active diagnostic code.
D. Verify that the latch tab of the connector is properly latched.
E. Check the allen head screw on the ECM connectors for the proper torque.
F. Check the harness and wiring for abrasions and for pinch points from the sensor to the ECM.
Expected Result: All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Test Step 2. Check for Active Diagnostic Codes
A. Connect Caterpillar Electronic Technician (ET) to the service tool connector. Read More: How to Connecting Caterpillar ET Software to the ECM.
B. Turn the keyswitch to the ON position.
C. Check for active diagnostic codes CAT ET. Record any active diagnostic codes. Note: Wait at least 15 seconds in order for the diagnostic codes to become active.
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| Figure 1.2 - Fuel Temperature Sensor: Voltage Above Normal |
code -04.
Test Step 3. Check the Pull-Up Voltage at the Sensor Connector
A. Disconnect the Fuel Temperature Sensor connector.
B. Turn the keyswitch to the ON position.
C. Measure the voltage between terminal 1 (sensor signal) and terminal 2 (sensor return) at the sensor
connector.
D. Turn the keyswitch to the OFF position.
Expected Result: The voltage is 5.5 ± 0.5 VDC. Read More: PULL-UP Voltage and How ECM Uses it to Determine Diagnostic Conditions.
Test Step 4. Create a Short at the Suspect Sensor Connector
A. Turn the keyswitch to the OFF position.
B. Install a jumper wire between terminal 1 and terminal 2 on the connector for the suspect sensor.
C. Connect the jumper on the harness side of the connector.
D. Turn the keyswitch to the ON position.
E. Check for active diagnostic codes Cat ET. Record any active diagnostic codes. Wait at least 15 seconds for activation of the short circuit diagnostic code -04.
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| Figure 1.3 - Fuel Temperature Sensor: Voltage Below Normal |
F. Remove the jumper wire.
G. Turn the keyswitch to the OFF position.
Expected Result: A short circuit diagnostic code -04 is active when the jumper wire is installed. An open circuit diagnostic code -03 is active when the jumper wire is removed.
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| Figure 1.4 - Fuel Temp Sensor Short (174-4) |
OK - The engine harness and the ECM are OK.
Repair - Temporarily connect a new sensor to the harness, but do not install the new sensor in the
engine. Verify that there are no Active Diagnostic Codes for the sensor. If there are no Active Diagnostic
Codes for the sensor, permanently install the new sensor (CAT P/N: 197-8391). Clear any logged diagnostic codes.
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