Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Intake Air Temperature Sensor

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OPERATION



The Intake Air Temperature (IAT) sensor is located inside of the volume air flow sensor box, attached between the air cleaner assembly and the air intake hose. The IAT functions by converting the temperature of the intake air into voltage, which is then fed to the ECM. The IAT sensor does this by taking the 5 volt power current, which is made by resistance inside the ECM, and grounding it back to the ECM. Before the current is grounded it passes through the IAT sensor, which is also a form of resistor, and is reduced by the resistance at an inverse proportion to the intake air temperature. In other words, the higher the intake air temperature, the lower the resistance of the IAT sensor. The ECM, based upon these signals from the IAT sensor, then corrects the amount of fuel injection and ignition timing.

Since the air temperature is measured after the air cleaner, the air has some chance to warm up. Therefore, the IAT sensor indicates a different temperature than the outside temperature.

HARNESS TESTING

The 1993-95, rear-wheel drive 2.4L (California) Pick-ups have the same engine controls as the 3.0L engines. All other 2.4L engines are listed as 2.4L engines.

  1. Unplug the wiring harness connector from the side of the Volume air flow sensor box, this harness connector also services the IAT sensor.
  2.  
  3. Attach the ohmmeter to the harness side connector on terminal 5 and check for continuity of the ground circuit. If there is any continuity, proceed to the next step, otherwise repair or replace the harness between terminal 5 and the ECM terminals 14 and 24 for 2.4L engines, terminals 17 and 24 for 3.0L (12 valve) engines, and terminal 72 for 3.0L (24 valve) and 3.5L engines.
  4.  
  5. This step is NOT for 2.4L engines, all other engines should do this step, however. Disconnect the ECM harness connector. Check for an open or short-circuit between the IAT terminal 6 and the ECM terminal 8 for 3.0L (12 valve) engines, or ECM terminal 52 for 3.0L (24 valve) and 3.5L engines. If there is a short or open-circuit, repair or replace the harness between these two terminals. After this test, plug the ECM harness connector back in.
  6.  
  7. Turn the ignition switch to ON and measure the power supply voltage from terminal 6 to ground. The voltage should be 4.5-4.9 volts, if this is the voltage measured then the IAT is OK. If the voltage is anything other than the specified voltage, repair or replace the harness between the IAT terminal 6 and the ECM terminal 8.
  8.  
  9. Plug all connectors back into place.
  10.  

COMPONENT TESTING



See Figure 1

  1. Unplug the volume air flow sensor connectors.
  2.  
  3. Measure the resistance between the volume air flow sensor/IAT sensor harness connector terminals 5 and 6. The resistance between these two terminals depends on their temperature. If the temperature is around 32°F (0°C) the resistance should be 6.0 kilohms, at 68°F (20°C) the resistance should be 2.7 kilohms, and with the temperature at 176°F (80°C) the resistance should be 0.4 kilohms.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Check the resistance between these two terminals-resistance should go down as temperature goes up

  1. Measure the resistance while heating the sensor with a hair drier. The higher the temperature (the hotter the IAT sensor), the smaller the resistance should become.
  2.  
  3. If resistance does not decrease as temperature increases or the resistance remains unchanged, replace the volume air flow sensor assembly.
  4.  

REMOVAL & INSTALLATION



See Figure 2

Since the IAT sensor is integral to the volume air flow sensor assembly, refer to the previously described removal and installation procedures for the volume air flow sensor.



Click image to see an enlarged view

Fig. Fig. 2: The Intake Air Temperature (IAT) sensor is located inside the volume air flow sensor assembly-all models similar

 
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