i had the snap on scanner hooked up to my car today and i noticed it reads the coolant temp and mat temp in celcius so i came on line and converted the mat temp. now my sensor is relocated to the air box and this is when the car had sat over night, it was 45* out, the scanner said 31* C which is 87* F, what gives? the air coming in cant be nearly that warm. and to prove this further i hooked up a 4.7K resistor to the mat plug and it read 14* C which is 57* F, 7* higher then what the 4.7K resistor should tell the computer. i had to run a 2.2K and 3.5K resistor in series to get 11* C which is 50* F. is this normal? why is my MAT sensor readings so far off, especially when plugged in?

 

Maybe the MAT sensor is bad? swap it for another one.

the resistor test sounds "close enough" to me. i'd swap the MAT and see how it goes.

You might want to read some of the other posts here (do a search), there has been discussion on what all the MAT sensor does and doesn't do on the MAF system.

 

ok i read that it controls the EGR valve. i have the EGR deleted, so does this mean that it does nuthing else but the egr valve. i thought it had to do with pulse width and stuff. someone help :-(

 

hopefully one of the experts will step in, but from what I remember of MAF conversations (which I don't pay much attention to since i'm SD), the MAT really doesn't do much of anything on your car except eGR enable/disable points and i think craig mentioned something about a startup fuel modification...

but essentially it doesn't do much of anything because the MAF sensor doesn't need to have it's value compensated for temp..

 

SD Mat has been said to have additional fueling beyond the VE tables

where as MAF cars it is primarily for EGR

 

Yes,
and depends on the code.

On the 31T MAF code the IAT is rather drastic at the extremes.

Then on some code as I recall the MAT is used as a default for a CTS failure.

In the 8D code there is a cranking fuel correction based on MAT.

But, some of this is subject to weither there is actual code to use what's in the tables switches settings.

 

The scanner may not be converting the MAT value correctly. Can you try a different brand scanner as a double check.

RBob.

 

Testing with a resistor makes me want to use the word 'tolerance'

fwiw

 

Winaldl doesn't have the correct algorithm for converting the raw ALDL CTS stream to *C (or *F) '808 ECM's. Check your data log if you're using Winaldl and see if the temperature scan result is high for your MAT when the engine is cool and low when it's hot. That's what happens on mine on the CTS: maybe MAT works like that on yours?

This is not a bitch about Winaldl- it's a fantastic free lunch. Joby says he'll fix it one day and I'm grateful to have it for nix now.

John