Dual Battery System And Relays
| Refer to COMPONENT INDEX . |
Dual batteries support vehicle operation and are charged in series. During ESS autostop or autostart events, the two batteries operate independently:
- The larger cranking battery supports the engine cranking events.
- The smaller auxiliary battery supports the vehicles electrical load during ignition ON, engine OFF ESS system events.
Both the primary cranking battery and the auxiliary battery operating parameters are managed by PCM ESS logic and are separated by a PCR.
If the auxiliary battery is disconnected, the PCM will set a DTC at Key ON. The PCM will then inhibit the ESS system until the DTC is cleared. The PCM will then bus a signal to display a telltale message on the IPC for the driver even if a different display menu is currently being used.
The PCM checks direct battery input which is wired from the auxiliary battery during an ESS autostart event and compares it to two calibrated thresholds within the PCM logic. If the battery input is lower than the first threshold, the PCM will inhibit ESS, such to allow the battery to charge for a calibrated engine run time, and displays a "Battery Charging" message in the ESS IPC menu, in addition to an incrementing a counter, if counter reaches its calibrated threshold, PCM will set a DTC and the PCM will then bus a signal to display a telltale message on the IPC for the driver even if a different display menu is currently being used and inhibit ESS until the DTC is cleared. If the battery input is lower than the second threshold then the PCM will set a DTC for a depleted Auxiliary battery and disable the ESS system. The PCM will then bus a signal to display a telltale message on the IPC for the driver even if a different display menu is currently being used.
Dual Battery Control Relay (DBCR) and Power Control Relay (PCR)
The DBCR is used by the PCM to control the PCR.
The PCR is a normally closed relay placed in between the cranking battery and the auxiliary battery and is used to isolate the two batteries from each other in order to avoid voltage dips when the starter cranks the engine during an ESS Autostart event.
The larger cranking battery is responsible for engine cranking. The smaller auxiliary battery is responsible for managing the vehicles electrical load demand during ESS cranking.
During ESS cranking events, the PCM commands the PCR to open for a calibrated time to isolate the Auxiliary battery.
When the ignition is cycled to the crank position the PCR relay is energize momentarily and will open the contact separating the two batteries. If the auxiliary battery is depleted the PCM resets and sends a message that ESS will be disabled. "Stop Start Not Available Battery Protection Mode" may be displayed in the IPC. In this case it is possible to see DTC "P00FD" in the PCM. If the battery is above 10 volts and below 12.6 volts when the vehicle starts a message that may appear, "Stop Start Not Available Battery Charging".
The DBCR is OBDII diagnosed for short to ground, short to battery and open circuit.
The PCR is also OBDII diagnosed for stuck open and stuck closed. For a stuck closed PCR, OBDII can determine faults based on voltage difference between Auxiliary battery and Cranking battery. If a stuck closed Diagnostic Trouble Code (DTC) is matured, the Powertrain Control Module (PCM) busses a signal for the IPC to display an ESS message to the driver. For a stuck open PCR, OBDII diagnostics can determine failure on voltage during Key ON Engine ON. If a stuck open DTC is matured, the PCM also busses a signal for the IPC to display an ESS message to the driver.