An IAT is a type of NTC thermistor like a ECT and a thermo fan switch which changes its resistance as it heats up sending different voltage signals to the ECU soit knows the air temperature through the intake.
I placed an IAT sensor in a bowl of water and gradually heated it up, when doing this i measured the resistance between the two terminals on the IAT as the water heated it up and recored the resistance at the different temperatures.
Temperature (degrees) | Resistance (K ohms) |
Room temp | 1.6 |
35 | 1.57 |
40 | 1.23 |
45 | 1 |
50 | 0.87 |
55 | 0.71 |
Engine: Toyota 1zz
On the 1zz i worked on the IAT was located just before the throttle body shown in the picture above.
With the engine not running i back probed the likely wire to be the IAT sensor's input wire and then switched the ignition "on" and measured the voltage going to this terminal and got a reading of 4.92 volts which is a correct voltage input to this IAT because it works on 5v but there was an internal resistance in the multimeter of 0.9 ohms. Th input reading of 4.92 at the IAT is similar to the ECT's reading of 4.5v which means they both run on a 5v supply from the ECU.
The IAT output reading affects the ECU's outputs for the fuel injection because the ECU needs to know the temp of the air coming into the intake so it knows how much fuel to inject e.g. if the air was cold the ECU would inject more fuel because it needs to warm up the engine to get to operating temperature. When the engine is warm it will change the temperature within the engine bay which will change the readings the IAT sends to the ECU because the air is warmer. If if the plug was loose or if the terminals were corroded it would cause the IAT to send incorrect signals to the ECU therefore effecting the overall operation of the engine.
The IAT output reading affects the ECU's outputs for the fuel injection because the ECU needs to know the temp of the air coming into the intake so it knows how much fuel to inject e.g. if the air was cold the ECU would inject more fuel because it needs to warm up the engine to get to operating temperature. When the engine is warm it will change the temperature within the engine bay which will change the readings the IAT sends to the ECU because the air is warmer. If if the plug was loose or if the terminals were corroded it would cause the IAT to send incorrect signals to the ECU therefore effecting the overall operation of the engine.
