PCM failure on 2001 Mercury Mountaineer

What would cause the PCM to fail? It has been replaced 5 times.

1 answer
A PCM should not fail repeatedly unless something is shorting it out. Is it the same circuit that blows each time say the fuel injectors or ignition coil supply? I have had a customer burn out an ECM on the same car twice, it is a car they don't use much and they jump started it backward twice in three years.
There are good and bad ECM re-builders out there as well if it is a remanufactured computer you have been using.