Intake Manifold Air Temperature Sensor - Voltage Below Normal

Intake Manifold Air Temperature Sensor

Figure 1.1 - FW Murphy (Mani Tmp Error)

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).

1). Connecting Caterpillar ET to the ECM (In this case: C-15 Engine). Read More: How to Connecting Caterpillar ET Software to the ECM.

2). Check for Active Diagnostic Codes (1), found Code: 172-4 (MID 036 CID 0172 FMI 04).
Figure 1.2 - Intake Manifold Air Temperature (Voltage Below Normal)
  • Conditions Which Generate This Code - The signal voltage from the inlet air temperature sensor dropped below 0.2 VDC for eight seconds. Read More: Sensor Diagnostics on Electronic Engines.
  • 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.

A). Perform the following diagnostic procedure:
  • Keyswitch to ON position, remove connector to Intake Manifold Air Temperature Sensor, and Check the pull-up voltage between terminal 1 (sensor signal) and terminal 2 (sensor return). In this case, pull-up voltage is OK (The voltage is 5.5 ± 0.5 VDC) and an open circuit diagnostic code -03 (172-3) is active at this time. Read More: PULL-UP Voltage and How the ECM Uses it to Determine Diagnostic Conditions.
Figure 1.3 - Intake Manifold Air Temperature (Voltage Above Normal)

B). Measure the resistance for the sensor (M ohms), also indicates an open circuit.
-Replace the sensor, with CAT P/N: 234-5013.

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