It depends. My guess on the pumps in the much colder climates is motor failure. Pumping the ATF when it becomes sludge just burns out the motor. It would be nice if Mitsu had some sort of fusing or time out on the motor (like just about ANY electrical motor has), that would protect it. Other failures include bad corrosion of the housing. This is the case in most northeast climates that get hammered with salt in the colder months. In that case bearings seize and seals begin to leak internally because the housing is badly corroded. I've religiously sprayed mine down about every month with some anticorrosion spray hoping to curb that as long as possible. It doesn't take them long to start to really oxidize badly. As far as valving, from the research I've done, those don't go bad that often. Solenoid valves are ridiculously simple and for one to go bad is probably unlikely. I've also read that the accumulators can loose pressure, so basically your pump is running overtime to try and keep up with demand. Roger Rally has outfitted pumps with larger capacity units to try and accommodate that issue. For a long term fix, a new fluid that is more stable at very low temps is necessary along with a housing that is more resistant to corrosion. Possibly an aftermarket housing machined from stainless or aluminum would be an option too.
You can do job yourself and I can overhaul your pump , you don't need lift but you will need to raise your passenger rear corner and remove wheel ( always work safe don't take chance ). Bleeding you may and may not need to do there is solution for that part as well
Many people on this forum have said that it's fine to drive the car without the ACD/AYC pump working. What is it that's bad about driving without the pump working?
