The OEM replacement is $370 shipped - that is a bit pricey... It is frustrating that you can't buy the controller solo.
Adding a touch of reverse engineering... The controller essentially has two sides to it. On one side, the high power circuitry (the FETs and back EMF protection Diode). On the other, we have the low power logic control. It is my guess that the severe overheat condition, originally caused by the "bad jump start", may have fried the logic control.
Additional testing revealed the FET gate is either too fast for my oscilloscope to measure (unlikely, but possible), or it is perpetually sitting at 0V due to a logic control failure. If it is just stuck at 0V, the FETs will never turn on and close the circuit to the cooling fan. I have ordered a $40 function generator from Ebay to generate a new gate signal, and an upgraded 120V capable oscilloscope.
It is now my intention to use the function generator to test the FETs themselves, manually - under the assumption that the low power portion of the board has died. This device was designed to never be taken apart, including ultra-high temp solder which my iron won't melt. So, removing the low power portion will fundamentally ruin the device, but who cares at this point?... However, with the knowledge I have obtained thus far, it might be possible to salvage the high power side of the board and design a new analog (or better yet microcontroller) based circuit board and place it in the same case.
If the existing FETs are proved to still be viable, I would likely choose the analog path initially just to get the vehicle back in full operating condition. Using an opto-isolator 4N25, I can isolate the ECU signal in case of failure (and fool the ECU into thinking the OEM controller is in use). Then, it should be a simple matter of providing a valid gate signal to the FETs. If I choose the microcontroller option, it is feasible to build in a case thermistor to sense compartment temperature and keep the engine bay a little better ventilated. (It gets hot and dry in SoCal). Ordering the OEM part will be a last resort.
It will be at least a week or so before I get my parts in, I will post back with results.
If anybody happens to know the name of the 2 pin fan connector, and/or the 3/4 pin harness connector, please let me know. I'd like to order plugs to make extension cables for the fan and harness.
Last edited by dmiles813; 02-04-2014 at 02:36 AM.