Alright, I don't want to do much, just want my cooling fans to kick in somewhere below the boiling point of water...(I know it's not exactly STP, but still...)

I know there is software, etc... in order to get into these computers... What I don't know is what form it takes, how much it costs, and what exactly I have to do to accomplish this. I have zilch experience in this particular area, so assume I'm we Todd did...:rolleyes:

IIRC the cooling fans have a mechanical temp switch in the head/intake somewhere that overrides the PCM programming. Stock is pretty high. Hypertech does have some that are set cooler, like around 190-200, but it is intended to be used with a cooler thermostat like a 160. A 160 is a tad cool to be efficient for the oil in the block, but it can be done. It is important to get the oil up high enough in temp to boil off moisture in the oil

As for programming the PCM, I don't know if much on it was ever cracked, not a huge amount of customers with Cadillacs wanting it. So the cost would likely be fairly high for the little you gain in it.

You could be really enterprising and make a op amp ckt that uses the PCM Coolant Temp Sensor and make it trigger the fan relays (3 of them, secondary, and 2 on primary for low speed and one for high speed). Would be fairly simple to do, but might be somewhat touchy to calibrate due to temp characteristics of the parts.

You could be really enterprising and make a op amp ckt that uses the PCM Coolant Temp Sensor and make it trigger the fan relays (3 of them, secondary, and 2 on primary for low speed and one for high speed). Would be fairly simple to do, but might be somewhat touchy to calibrate due to temp characteristics of the parts.

Hmmm...I do wish I had a clue how to do so lol. But I'm guessing start with a wiring diagram here... Perhaps I'm complicating it though... Are you just saying hotwire the fan relays in a circuit with the coolant temp sensor (like right off the wires from it?), and put resistors along the wiring until I find the right voltage to trigger the fans at the temperatures I want? Sounds touchy indeed lol...

Hmm...actually it just seems like it wouldn't be quite that simple...but err...*shrug* :-D

OBD I computers usually contain pluggable PROMs.
They can be programmed but you have to have special hardware including the stuff to erase the chip, under the label is the chip itself and I think it's infa-red that resets all the transistors for programming.
I think your other poster there is right, most of the older ones used an external switch and a relay to control the cooling fans.
Reprogramming the PROM wouldn't do you much good.
On OBD-I most people would just buy a pre-programmed PROM and plug it in to the computer for any sort of mod.

There are the 3 relays. 1 small fan, 2 large fan, speed 1 and speed 2. The PCM AND fan switch (override) connect to the ground side of the relay, so at anytime either can kick the relay on and turn the fan on.