Temperature Gauge Dampening
Courtesy Of 97EldoCoupe
I've been going through some old service manuals I have. This; due to my '97 STS having an over voltage condition that blew out the PCM....
Section 8C1-8 of the 1996 Service Manual Book 1.
This says it. Think about what the smoothing filter would do provided there was quick temp spikes or changes. Think about the fact that it uses a 16 point calibration table. One degree of temperature change would be the difference between the IPC commanding the needle to move to the next 16th position or not. This gives a lot of room for variances between cars. Very easily. So after a head gasket job is complete; if the vehicle ran one degree hotter or cooler; this one degree could be the difference between the gauge needle moving past 12:00 or not.
Coolant temperature is broadcast from the PCM via Class 2 serial data to the IPC. The IPC compares the temperature data with a sixteen-point calibration table to determine needle deflection. A smoothing filter is used to secure a continuous response.
This is out of the 1996 manual; but keep in mind Cadillac retained a lot of the same electronic engineering through many years and models.
I don't know if this has ever been found by another forum member or not; but if possible; Ranger; please Sticky this somewhere for future reference. This has been of topic for a while; and short of talking to the original engineers; this may be the most in-depth information on the subject we will ever come up with.
Also the smoothing filter; since we now know one is used; may be programmed different through the years and models. Doubtful but easily possible.