Charging System

The Powertrain Control Module (PCM)-controlled, or Smart Charge charging system determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator. The Smart Charge charging system is designed to set 1 of 6 Diagnostic Trouble Codes (DTCs) any time a charging system fault is present. All of the Diagnostic Trouble Codes (DTCs) can set continuous faults, but not all Diagnostic Trouble Codes (DTCs) set as on-demand faults.

This system uses 2 communication lines between the Powertrain Control Module (PCM) and the generator/voltage regulator. Both of these communication lines use Pulse-Width Modulation (PWM). The generator communication (GENCOM) line communicates the desired setpoint from the Powertrain Control Module (PCM) to the voltage regulator. The generator monitor (GENMON) line communicates the generator load and error conditions to the Powertrain Control Module (PCM). The GENCOM command is only sent by the Powertrain Control Module (PCM) when it is necessary to adjust the voltage setpoint. If the setpoint does not need to be changed, several seconds may elapse between Powertrain Control Module (PCM) GENCOM commands. This normal operation appears in the Parameter Identification (PID) as occasional bursts of pulse-width commands. The third pin on the voltage regulator, the "A" circuit pin, is a circuit dedicated to monitor or sense battery voltage.

The Powertrain Control Module (PCM) simultaneously controls and monitors the output of the generator. When the current consumption is high or the battery is discharged, the Powertrain Control Module (PCM) raises engine speed as needed to increase generator output. 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 Powertrain Control Module (PCM) is able to adjust the charging voltage according to the battery temperature by using a signal from the Intake Air Temperature (IAT) sensor. The Powertrain Control Module (PCM) also uses other inputs to control charging system voltage such as the Vehicle Speed Sensor (VSS) and Engine Coolant Temperature (ECT). The voltage setpoint is calculated by the Powertrain Control Module (PCM) and communicated to the voltage regulator by the GENCOM circuit based on the needs of the vehicle and the conditions.

The Powertrain Control Module (PCM) turns off the generator during cranking to reduce the generator load and improve cranking speed. Once the engine starts, the Powertrain Control Module (PCM) slowly increases generator output to the desired voltage.

The Powertrain Control Module (PCM) reports any charging system faults and sends a message through High Speed Controller Area Network (HS-CAN) to the Body Control Module (BCM). The Body Control Module (BCM) controls the charging system warning indicator by sending a message over the Medium Speed Controller Area Network (MS-CAN) to the Instrument Panel Cluster (IPC). The Instrument Panel Cluster (IPC) then controls charging system warning indication based on the message from the Powertrain Control Module (PCM) through the Body Control Module (BCM). The status of the Powertrain Control Module (PCM) charging system warning indicator and/or message can be confirmed by viewing Powertrain Control Module (PCM) Parameter Identification (PID) generator fault indicator lamp (GENFIL). Any charging system fault detected by the Powertrain Control Module (PCM) results in 1 or more Diagnostic Trouble Codes (DTCs) being set and the Parameter Identification (PID) GENFIL having a status of On. If equipped with a charging system warning indicator, the Instrument Panel Cluster (IPC) turns the indicator on or off. If equipped with a message center, the Instrument Panel Cluster (IPC) displays a CHECK CHARGING SYSTEM message. When the ignition is ON and the engine is off on vehicles equipped with a message center, the CHECK CHARGING SYSTEM message may not be displayed.

Under certain circumstances, the charging system may have a concern, but still keeps the battery charged and the vehicle running. GENCOM is normally used to initiate charging, but the generator may charge with a fault in this circuit. If the engine operates at more than 2,000 Revolutions Per Minute (RPM) momentarily, the generator may self-excite or start charging on its own. The charging system warning indicator is illuminated and/or CHECK CHARGING SYSTEM message is displayed, and the generator operates in a default mode (approximately 13.5 volts) until the engine is turned off. When the engine is restarted and the engine operates at more than 2,000 Revolutions Per Minute (RPM) momentarily, the generator may again self-excite and again the charging system warning indicator is illuminated and/or CHECK CHARGING SYSTEM message is displayed.

The Parameter Identifications (PIDs) and their associated descriptions used in the charging system diagnosis are listed below: