Have a 2003 Saturn L200. As soon as Engine Code P0113 IAT Sensor 1 Circuit High Input triggers, the radiator fans go to max power and strangely the automatic transmission shifts VERY hard. The jolt in gear changes is hard enough to make me think it will break something eventually.
When I clear the OBDII code the problem goes away - fans speed normal, smooth shifting. After 20 minutes of driving code triggers and problem comes back.
I put in a new Air Intake Temp sensor and cleared the OBDII codes. Again it ran fine.. hopes were up... then engine light came on.. P0113 again, fans high speed, hard shifts.
The intake air temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The powertrain control module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively high IAT signal voltage, indicating a low temperature, DTC P0113 sets.
Conditions for Setting the DTC
The PCM detects that the IAT sensor parameter is less than -39°C (-38°F) for more than 3 seconds.
Check for a break in the connector or wiring that corresponds to high resistance in one of the two wires to the iat sensor.
If the circuit is open then the resistance seen by the PCM is infinite which is interpreted as a really low temperature
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derf - Thanks for the quick response. I checked the wiring, what I could see anyway. Nothing obvious. I also removed the connector from the IAT sensor and meaured the voltage pin to pin inside the connector - 7.6 volts (car off with key turned to run). As you said one pin is high at 7.6v the other is ground.
What I find strange is that when I clear the ODBII code the problem goes away for 10 - 20 minutes of driving. If the problem was a broken wire or bad ground, how would clearing the code fix if temporarily?
If a broken or loose wire is still the most likely cause, I will dig in deeper checking wiring. It is difficult with all the wiring harnesses, as I am sure you know.
derf - A small nick in one of the wires at the Air Intake Sensor seems to have been the problem. I soldered in a new piece of wire, cleared the code and it is fixed: After 4 days PO113 IAT code has not come back, or any engine codes,and the hard shift / high fan speed is gone.
Amazed that this could have caused it. Photo of nicked wire is attached.