IAT voltage test

[spec_ops57]

I've narrowe my IAT sensor down to two plugs, is there a certain voltage that runs through it that I could see by using a fluke meter (multimeter) or is there a ohm rating or anything like that?

[Crasen]

[quote=spec_ops57]I've narrowe my IAT sensor down to two plugs, is there a certain voltage that runs through it that I could see by using a fluke meter (multimeter) or is there a ohm rating or anything like that?[/QU

Most sensors will typically have a 5 volt reference voltage, although a sensor with a 12 volt reference voltage is not unheard of, if there is say three wires , one would be the 5 volt reference voltage one would be a ground and one would be a signal wire back to the ecm, if there is a wire with a green tracer stripe on it I would bet that is the signal wire. I wish I could tell you more but I haven't had a Ranger in Over a year so details are not that fresh

[stuzman]

Originally Posted by spec_ops57

I've narrowe my IAT sensor down to two plugs, is there a certain voltage that runs through it that I could see by using a fluke meter (multimeter) or is there a ohm rating or anything like that?

Okay, I'm not sure what you mean by narrowing it down to two plugs; maybe you mean there's two wires going to the sensor. In any event, you can check the sensor using voltage or resistance. First, a little about what they are and how it works in case you or someone else doesn't know. The incoming air temperature (IAT) and engine coolant temperature (ECT) sensors are both thermistors as they're called in the electronics field. This is a resistor which varies its resistance according to the air or coolant temperature. When the temperature of the medium is low, the resistance of the sensor is high and when the temperature of the medium is high, the resistance of the sensor is low. So, the temp and resistance are inverse of each other. These sensors are known as having a negative coefficient. There are other thermistors that have a positive coefficient which behave backwards from the above. Now that you know what they are, it helps to know how they work in the circuit.

The thermistor is a two wire device where one lead is fed a reference voltage of 5VDC from the PCM (this voltage doesn't change; the reason for calling it a reference). The other wire from the sensor goes back to the PCM where it is measured. The PCM can calculate the temperature of the medium by knowing the voltage on its signal wire. As a quick example, let's say the PCM is measuring a very low voltage such as 0.2VDC. Now with that low a voltage, you would know that the resistance of the sensor would be low (meaning a high medium temp) and if it was say 3.5VDC on the signal wire, then the resistance of the sensor would be high (meaning a low medium temp). So, you need a chart which will correlate the temperature of the medium with the voltage and/or resistance of the sensor. The chart below can be used for the IAT or the ECT. The first column is the temp of the medium in Fahrenheit, second column is the voltage measured on the signal wire back to the PCM and the third column is the resistance of the sensor in Kilo Ohms.

248F = 0.27VDC = 1.18K ohms
230F = 0.35VDC = 1.55K ohms
212F = 0.46VDC = 2.07K ohms
194F = 0.60VDC = 2.80K ohms
176F = 0.78VDC = 3.84K ohms
158F = 1.02VDC = 5.37K ohms
140F = 1.33VDC = 7.70K ohms
122F = 1.70VDC = 10.97K ohms
104F = 2.13VDC = 16.15K ohms
86F = 2.60VDC = 24.27K ohms
68F = 3.07VDC = 27.30K ohms
50F = 3.51VDC = 58.75K ohms

You can also connect a pot in place of the sensor and set it to one of the resistance values in the table to correspond to the temperature of the medium to see if the engine's performance improves.

Good luck with the repair and keep us posted on your results!

[spec_ops57]

There's two plugs on the intake that looked to be close to IAT's in a diagram I got (it only had one labled) but the one is a 2 wire red/black, and the other one is a 4 wire all grey. I'm certain it's the two wire plug so I'm gonna put my resisitor on it and let you guys know how it goes