GM Coolant Temp Sensor

[peter paul fenske]

Hi All
FYI
The 730 ECM GM uses and others use two pullup resistors in their
scheme to linearize their tempeture sensor. This sensor turns
out to be a thermistor with a neg temp coef. When cold up to 
about 122 degrees a 348 and 3.65K resistor are used. This matches
to sensor linearity from about 80 to 122 degrees with an error of 
about 1%. When the ECM senses 122 degrees from the A-D the 
348 ohm resistor is switched in. There is less than 1% deviation
from straight line between 122 and 250 degrees. True a bit of 
code with breaks and a shift right(/2) must be used but for
most a correction table is necessary only below70 degrees.
This results in hex values 0-255 representing temp in celsius.

Well Tnx all: peter