MEFI Fuel Injection
IAT Circuit IAFM Engines
8.1L Engines
The ECM sends out 5 volts to the sensor on the signal wire. As the temperature of the sensor changes, it’s resistance changes. As the sensor’s resistance decreases, the current flow in the circuit increases. As the current increases, the voltage drop across the fixed resistor in the ECM increases. This causes the voltage available at the A/D converter (between the fixed resistor and the sensor) to be lower as the sensor’s temperature rises. An open circuit in either the signal wire or the sensor return will set a “voltage high” fault. A “voltage high” fault is also a “low temperature indicated” fault. The EFI manual has temperature/resistance charts for both the ECT and the IAT sensors. These charts are located at the DTC test for the fault.
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