Principles of Operation

PRINCIPLES OF OPERATION

This vehicle is equipped with a PCM-controlled charging system, which determines the optimal voltage setpoint 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 (GENCOM) line communicates the desired setpoint from the PCM to the voltage regulator. The generator monitor (GENMON) 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 PCM uses a calibratable algorithm to estimate battery temperature and to reduce battery damage caused by over and under charging. Using this algorithm, the PCM determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator on the GENCOM circuit. While this is occurring, the PCM is also monitoring the GENMON circuit for charging system information, such as transient electrical loads or errors.

If the PCM senses when the charging system receives a transient electrical load (which may cause poor idle quality, such as an idle roll) the PCM can then adjust the injectors opening time to account for the transient electrical load. In this manner, the PCM can maintain a consistent idle speed.

If the PCM detects a charging system error, it broadcasts a CHARGING SYSTEM STATE STATUS message through the controller area network (CAN) communication link, causing the instrument cluster to illuminate the charging system warning indicator. The charging system warning indicator is illuminated if the PCM fails to see a signal on the GENMON circuit for a time period greater than 500 ms. This telltale is used to indicate over-voltage conditions detected by the PCM.

The PCM also reduces the mechanical load on the starter by initially commanding a low voltage setpoint (using the GENCOM circuit) in order to improve start times and reduce load on the starter and its related system.

Each time the key is cycled to the ON position, the instrument cluster initiates a bulb check by illuminating the charging system warning indicator. This operation is called prove-out. The PCM then issues a CHARGING SYSTEM STATE STATUS - OK message if the charging system is functioning correctly. This message is sent once the engine is running and the charging system is determined to be operating correctly. If the cluster does not receive an OK message, the cluster lights the charging system warning indicator indefinitely. Vehicles equipped with a message center display CHECK CHARGING SYSTEM any time a charging system error is present.

This is a System 4 charging system, which uses the GENMON and GENCOM 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. System 4 charging systems may use any type of generator, as the generator type usually depends on the engine packaging and/or output requirements versus cost.