Principles of Operation

The powertrain control module (PCM) controlled charging system determines the optimal voltage set point for the charging system and communicates this information to the voltage regulator. This system is unique in that it has 2 unidirectional communication lines between the PCM and the generator/regulator. Both of these communication lines are pulse-width modulated (PWM). The generator communication (GEN COM) line communicates the desired set point from the PCM to the voltage regulator. The generator monitor (GEN MON) line communicates the generator load and error conditions to the PCM. The third pin on the voltage regulator, the A circuit pin, is a dedicated battery voltage sense line.

The charging system voltage is controlled by the PCM. The generator charges the battery and at the same time supplies power for all of the electrical loads that are required. The battery is more effectively charged with a higher voltage when the battery is cold and a lower voltage when the battery is warm. The PCM is able to adjust the charging voltage according to the battery temperature by using a signal from the intake air temperature (IAT) sensor. This means the voltage set point is calculated by the PCM and communicated to the regulator by a communication link.

The PCM simultaneously controls and monitors the output of the generator. When the current consumption is high or the battery is discharged (the PCM recognizes this and increases the output of the generator to accommodate), the system is also able to increase the idle speed to increase the charge.

To minimize the engine drag when starting the engine, the PCM does not allow the generator to produce any output until the engine has started. The PCM then progressively increases the output of the generator.

The PCM turns the charging system warning indicator off after the engine is started and illuminates it under fault conditions (when the generator is not generating the correct amount of current with the engine running). The charging system warning indicator is also illuminated by the PCM whenever the key is ON with the engine OFF.

This is a System 4 charging system, which uses the GEN MON and GEN COM lines to control and monitor the charging system through the PCM. System 4 charging systems are virtually identical in design and therefore, share the same diagnostics. The circuit numbers and colors may be different, but the functions are the same.