Engine computer is the Powertrain Control Module. It has the voltage regulator built in.
When the problem acts up, measure the voltages on the two small terminals on the back of the alternator. They could be two plugged-in wires or two small nuts next to a black plastic block. One of those will have full battery voltage when the engine is running. The secret to diagnosing this system is the voltage on the other nut. If it is 0 volts, the brushes are open. If it is the same as the first terminal, the voltage regulator in the PM could be bad but more likely the wire going to it is open. If that part of the system is working the voltage will be less than the first terminal.
Thursday, January 13th, 2011 AT 7:02 PM