Voltage Signal: Description and Operation

BATTERY VOLTAGE - PCM INPUT
In order for the PCM to operate, it must be supplied with battery voltage and ground. The PCM monitors the direct battery feed input to determine battery charging rate and to control the injector initial opening point. It also has back-up RAM memory used to store Diagnostic Trouble Codes (supply working DTCs). Direct battery feed is also used to perform key-OFF diagnostics and to supply working voltage to the controller for OBD II.

The 5 and 8 volt regulators are protected from shorts to ground. This protection allows diagnostics to be performed should the 5 volt power supply become shorted to ground at any of the sensors. A short to ground in the 5 volt power supply will cause a "no-start" situation. There is a Diagnostic Trouble Code (DTC) if the 5 volt power supply becomes shorted to ground. Refer to the Diagnostic Procedures for more details on any on-board diagnostic information.

If battery voltage is low the PCM will increase injector pulse width (period of time that the injector is energized).

The direct battery feed to the PCM is used as a reference point to sense battery voltage.

Effect on Fuel Injectors
Fuel injectors are rated for operation at a specific voltage. If the voltage increases, the plunger will open faster and further (more efficient) and conversely, if voltage is low the injector will be slow to open and will not open as far. Therefore, if sensed battery voltage drops, the PCM increases injector pulse-width to maintain the same volume of fuel through the injector.

Charging
The PCM uses sensed battery voltage to verify that target charging voltage (determined by Battery Temperature Sensor) is being reached. To maintain the target charging voltage, the PCM will full field the generator to 0.5 volt above target then turn OFF to 0.5 volt below target. This will continue to occur up to a 100 Hz frequency, 100 times per second.