Volts Indicator

The Volts indicator (red) will be illuminated under the following conditions:
^ Lamp Terminal pulled low:
- Key On (Bulb check)
- Open Field or Regulator Circuit
- Output voltage above overvoltage set point (no control)
- Low system voltage above Engine RPM calibrated value (Undervoltage)
- Open P terminal at the Voltage Regulator, shorted positive or negative bridge diode at P terminal Field terminal voltage
- Condition indicate a voltage regulator disconnect (Low Duty Cycle)

The Powertrain Control Module (PCM) will determine Engine RPM, Generator Field Duty Cycle, Lamp Terminal State, L term disabled and send these as Class 2 messages to the Body Function Controller (BFC). The Body Function Controller (BFC) will then dictate to the Instrument Cluster the state of the Volts indicator and set the appropriate fault codes.

There are four fault codes possible that will illuminate the volts indicator.

The Lamp Terminal Open/Short fault and the Field Terminal Short fault and their respective codes can only be set and cleared with Ignition 1 active and zero engine RPM. Since the volts indicator is illuminated with Ignition 1 active and zero engine RPM the faults that can occur under these conditions cannot be communicated to the driver. Therefore, if either of these codes are set when the engine is started the indicator will remain illuminated to indicate the fault. The Lamp Terminal Open/Short program checks for a high lamp state while the Engine in not running. The Field Terminal Short program checks for a duty cycle higher than a calibrated value while the engine is not running. Both of these faults have a calibratable timer before setting.

The Field terminal fault and the Lamp terminal fault and their respective codes can only be set and cleared with the engine running. The Body Function Controller (BFC) will diagnose a possible voltage regulator disconnect (Field terminal fault) by monitoring the duty cycle and verifying it does not fall below the calibrated value for a calibrated time. The Lamp terminal fault is set if the Lamp terminal goes low for a calibrated time.

The volts algorithm tracks whether or not the Powertrain Control Module (PCM) has disabled the Generator on a cold start or in a stall condition and will not set any field or lamp faults. The Powertrain Control Module (PCM) will not disable the generator for more than 10 seconds.

In the event of a Powertrain Control Module (PCM) or a Body Function Controller (BFC) Class 2 or Serial Peripheral Interface (SPI) serial data loss the Volts indicator will remain in its last state prior to the loss of serial data.