Principles of Operation

WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.

After the engine is started, voltage is applied through the I circuit 904 (LG/RD) from the powertrain control module (PCM) to the voltage regulator. This turns the regulator on, allowing current to flow from the battery sensing A circuit 35 (OG/LB) to the generator field coil. At this time, the generator begins to generate current which is then supplied to the vehicle's electrical system through the output (B+) terminal of the generator.

Once the generator begins generating current, a voltage signal is taken from the generator stator and fed back to the regulator. This voltage feedback signal (typically half the battery voltage) is used by the regulator to provide a signal to the PCM. This, in turn, provides a signal over the CAN communication link to the instrument cluster to turn off the charging system warning lamp. This indicates the charging system is operating properly. The S (Stator) circuit is internal to the generator on the 4.6L applications and 4.0L applications built to December 8, 2003; and is an external circuit 4 (WH/BK) only on the 4.0L applications built from December 8, 2003.

With the system functioning normally, the generator output current is determined by the voltage of the A circuit 35 (OG/LB). The A circuit 35 (OG/LB) voltage is compared to a set voltage internal to the regulator, and the regulator controls the generator field current to maintain the correct generator output.

The set voltage will vary with temperature and is typically higher in cold temperatures and lower in warm temperatures. This allows for better battery recharge in the winter and reduces the chance of overcharging in the summer.