does anyone have an idea as to why my mat sensor is telling my computer -58 degrees. I'v checked the wires and they appear ok... i changed the sensor and still get the same reading..any thoughts?
Also i read somewhere in this forum that the mat sensor and the coolant sensor that mounts in the intake (not the single wire one that mounts in the head) are the same sensor...is this true?

 

You have a MAT or IAT sensor, that measures the temp of the incoming air, that one is in the intake tract somewhere; you also have a Coolant Temp Sensor, that measures the temp of {drum roll please} the coolant, usually located in the water outlet where the upper radiator hose goes; the sensor in teh left head is the one for the gauge; the one in the right head is the fan switch.

A disconnected wire to any of the sensors (not the fan switch) looks to the ECM like the lowest possible temp that it can understand.

Are you sure it's the air temp sensor that the ECM thinks is open, not the coolant temp?

 

As for them being the same sensor, you're partly correct. The CTS and MAT sensors on earlier TPIs were identical - the same part number. However, there were still two sensors. One senses coolant temperature at the front crossover in the intake base, and the other measures plenum air temperature and is screwed into the bottom of the plenum. There isn't a single, "dual-duty" sensor.

Later IAT (Intake Air Temperature) sensors had a more exposed sensing element to react to air temperature changes more quickly, and were mounted in the intake ductwork instead of the bottom of the plenum. This type sensor wasn't sealed well enough to survive in coolant temperature service, so a different part number was used.