SPN 105 - FMI 4 (Diagnostic Code: Intake Manifold Air Temperature Sensor - Voltage Below Normal)

SPN 105 FMI 4
Intake Manifold Air Temperature Sensor

Figure 1.1 - SPN105 FMI4 (Murphy PowerView)

MID 036 CID 0172 FMI 04
Conditions Which Generate This Code:
The signal voltage from the Inlet Air Temperature Sensor dropped below 0.2 VDC for eight seconds.

System Response:
The Electronic Control Module (ECM) will log the diagnostic code. The ECM flags Inlet Air Temperature as invalid data and a default value of 85 °C (185 °F) is used.

Possible Performance Effect:
Low power

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 Intake Manifold Air 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.
Figure 1.2 - Intake Manifold Air Temperature (Voltage Below Normal)
D. Determine if the problem is related to an open circuit Diagnostic Code -03 or a short circuit Diagnostic Code -04.

Test Step 3. Check the Pull-Up Voltage at the Sensor Connector
A. Disconnect the Intake Manifold Air 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
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. Disconnect the Suspect Sensor in Order to Create an Open Circuit
A. Turn the keyswitch to the OFF position.
B. Disconnect the Intake Manifold Air Temperature Sensor from the harness at the sensor connector.
C. Turn the keyswitch to the ON position. Wait at least 15 seconds for activation of the Diagnostic Codes.
Figure 1.3 - SPN105 FMI3 (Murphy PowerView)
D. Check CAT ET for an active open circuit Diagnostic Code -03 for the suspect sensor.
Figure 1.4 - Intake Manifold Air Temperature (Voltage Above Normal)
E. Turn the keyswitch to the OFF position.
Expected Result: An open circuit Diagnostic Code -03 is now active for the suspect sensor.
OK - A short circuit Diagnostic Code -04 was active before disconnecting the sensor. An open circuit
Diagnostic Code -03 became active after disconnecting the sensor.
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. Clear any logged diagnostic codes. Verify that
the repair eliminates the problem (CAT P/N: 234-5013).
Figure 1.5 - Inlet Air Temperature (115 deg F)

#Trip points for the Monitoring System
The Monitoring System determines the level of action that is taken by the Electronic Control Module
(ECM) in response to a condition that can damage the Engine. When any of these conditions occur,
the appropriate Event Code will trip.
Figure 1.6 - High Engine Inlet Air Temperature (Monitoring System)

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