Principles of Operation

PRINCIPLES OF OPERATION

The powertrain control module (PCM) controlled charging system 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 circuits between the PCM and the generator/regulator. Both of these communication circuits are pulse-width modulated (PWM). The generator communication (GEN COM) circuit communicates the desired setpoint from the PCM to the voltage regulator. The generator monitor (GEN MON) circuit communicates the generator load and error conditions to the PCM. The third circuit on the voltage regulator, the A circuit, is a dedicated battery voltage sense circuit.

The charging system voltage is controlled by the PCM. The generator charges the battery, and at the same time supplies voltage 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 setpoint is calculated by the PCM and communicated to the regulator by the GEN COM circuit.

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 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 is responsible for turning the charging system warning indicator off after the engine is started and illuminating it under fault conditions (when the generator is not generating the correct amount of current/voltage 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 circuits 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.

Circuit Description

Positive Battery Output (B+) Terminal Circuit SDC14 (RD)
The generator output voltage is supplied through the positive battery (B+) output terminal circuit SDC14 (RD) on the rear of the generator to the battery and electrical system.

Circuit SBB18 (YE/RD) for 2.3L and 3.0L, SSB17 (RD) for 3.5L
This is the A terminal battery voltage sense circuit and is used to sense battery voltage.

Circuit CDC15 (VT) (GEN MON)
This is the GEN MON circuit. The PCM monitors this circuit to determine the generator load and error conditions to the PCM.

Circuit CDC10 (BU/OG) (GEN COM)
This is the GEN COM circuit. The PCM determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator through the GEN COM circuit.