So I've recenlty bought used a 97 Ranger, I've been replacing things here and there (water pump, alternator bearings, idler tensioner, brake lines tensioner pulley). However, I recently got a check engine light I've been trying to diagnose that's not making any sense. I'm getting a P0113 (Intake Air Temp 1 Cricuit High). I look at the data stream and the IAT sensor is reading somewhere around 210 - 220 degrees F. Of course this is incorrect, first thing I do is replace the sensor. I picked up a Carquest IAT sensor from Advance Auto WTA1084, new sensor fits perfectly and upon looking at the datastream again I'm still getting somewhere around 210 - 220 degrees F. I pulled the sensor out while the engine is running and it reads -40 (normal). I put the sensor back in and I'm getting around 220 F. I then starting looking at my wiring. I did some research and wiring diagrams say the computer puts out around 5V to the sensor and the resistance is used to measure temp. I measure the voltage in the sensor harness and I'm getting around 4.6V (I guess normal). While the vehicle is off I use my ohm meter to probe each terminal on the IAT sensor harness to ground and it seems neither are touching round nor are they touching each other. I then pull the PCM (computer) harness plug at the firewall and trace the pin locations for the IAT sensor and measuresd resistance from the computer plug to the IAT plug and I'm getting 0 ohms each terminal from the IAT to each of the pins from the computer harness. Meaning they shouldn't be any shorts in the wiring harness from the IAT plug to the computer at least. This dosen't rule out a comptuer issue, but I have a hard time beliving the computer can fail in this way. I got more curious and literally pulled the computer out from the firewall and then opened the comptuer up to see if there could've been any water infultration etc or damage, the circuit board looked pristine with no water damage and the conforma coating was still intact.

I've done the following.
1. Tried two different scan tools (both showing the same)
2. Both the OLD IAT sensor and NEW one branded carquest are showing around 200ish F. I ordered and tried another NEW carquest IAT sensor and it's showing the same.
3. Thinking it could be variations in the sensor I've ordered a new Motorcraft MOT DY735 (2 terminal sensor) which I'm thinking is what my vehicle came with.
4. Tired with sensor out from the intake, engine cold/hot dosen't matter get similar results.








4. Traced the wiring from the IAT sensor plug all the way to the PCM harness plug and Ohmed them to be 0 ohm each with no apparent shorts.