It sounds like you have a battery temperature sensor that has gone out or have corroded wiring. Here is the alternator wiring diagrams below with a guide so you can do some testing and get back to us.
Here is a description of the voltage regulator and you have no alternative except to replace the PCM if the voltage regulator is bad.
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the Powertrain Control Module (PCM). The EVR is not serviced separately. If replacement is necessary, the PCM must be replaced.
The amount of DC current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series with the generators second rotor field terminal and its ground.
Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature. It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 100 times per second (100 Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output. Also refer to OPERATION for additional information.
Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.
Images (Click to enlarge)
Saturday, November 6th, 2010 AT 3:18 PM