85 Z28 with a stock 5.0 L TPI setup and computer. I logged the data tonight with WinALDL and captured all the data streams with no problems. Everything looks good except for the MAT:

The RAW:MAT column shows data starting at 178 and going to 194 (the car was warmed up when I collected the data). However, the SENSOR:MAT column shows only zero's. I have a code 23 set (low MAT), although the Check Engine light is not on. The code 23 comes up when the car is stopped on a cold morning. Once you start moving, the Check Engine light goes out. After the car warms up, no more Check Engine lights. Is this old error making the computer ignore raw MAT data, even though it's present?

Any insights would be greatly appreciated.

 

The ECM will use a default value for many sensors if it thinks the sensor is bad. But this needs to be a current error, not from one stored in memory.

A MAT low can also be caused by an open wire or connector at the MAT. Of course the MAT could also be bad.

RBob.

 

This is why I'm confused. The data in the RAW:MAT column seems to be coming in just fine and the numbers look very reasonable for the engine temperature. If the sensor is sending data, why is the SENSOR:MAT column showing only zero's?

I thought that the data flow looks like this:

MAT sensor <-----> ECM, RAW data ---(data processing)----> ECM, SENSOR data

Is this correct?

 

Your data flow is correct. It may be that the file WinALDL uses to dechiper the data is incorrect.

OTOH, the ALDL stream typically only provides the raw sensor data. So an actual MAT value would need to be produced by WinALDL from a lookup table.

RBob.

 

I'm sure that you're right. I thought that it was the ECM that sent the interpreted MAT value, but it would make much more sense for that translation to be handled by WinALDL. Thanks for the clarification.