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 the overvoltage set point (no control)
- Low system voltage above the engine RPM calibrated value (under voltage)
- Open P terminal at the voltage regulator, shorted positive or negative bridge diode at the P terminal
^ Field terminal voltage
This condition indicates a voltage regulator disconnect (low duty cycle)

The PCM will determine the following items:
^ Engine RPM
^ Generator PWM
^ Lamp terminal state
^ L term disabled

The PCM will send these as class 2 messages to the BCM. The BCM will perform the following functions:
1. Dictate to the instrument cluster the state of the volts indicator
2. Set the appropriate fault codes There are four codes possible with the volts indicator algorithm.

The lamp terminal open/short fault and the field terminal short fault and their respective codes may only be set and cleared under the following conditions:
^ When Ignition 1 is active
^ With zero engine RPM

Since the volts indicator is illuminated with Ignition 1 active and zero engine RPM, the faults that may occur under these conditions cannot be communicated to the driver. If either of these codes are set when the engine is started, the indicator will remain illuminated in order to indicate the fault. The lamp/terminal open/short program inspects for a high lamp state while the engine is not running. The field terminal short program inspects for a duty cycle higher than a calibrated value while the engine is not running. Both of these faults have a timer than may be calibrated before setting.

The field terminal fault and the lamp terminal fault and their respective codes may only be set and cleared with the engine running. The BCM will diagnose a possible voltage regulator disconnect (field terminal fault) by monitoring the duty cycle and verifying that 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 PCM has disabled the generator on a cold start or in a stall condition. The volts algorithm will not set any field or lamp faults. The PCM will not disable the generator for more than 10 seconds.

In the event of a PCM or a BCM Class 2 or an SPI serial data loss, the volts indicator will remain in the last state prior to the loss of the serial data.