System Operation - Standard Starting System

DESCRIPTION 

The Keyless Go system replaces the conventional key and ignition switch with a momentary press button and a wireless electronic key fob. When the operator presses the Go button, the RFH receives the request from the KIN and then looks for the valid key fob by using the LF antennas. If the RFH detects a valid key fob and the brake is engaged, the RFH sends a Controller Area Network (CAN) request to the BCM to change the ignition position to START/CRANK. The BCM controlled relay (starter relay 2) and PCM controlled relay (starter relay 1) are closed allowing the starter motor to engage.

The Powertrain Control Module (PCM) is the main module controlling operation of the starting system relays. There are two starter relays wired in series controlling starter motor operation. One is controlled by the Body Control Module (BCM) when commanded and the other is controlled by the PCM. When both relays are energized, a 12 volt feed is supplied to the starter solenoid, which will activate the starter. On vehicles that come equipped with the eTorque system, the initial engine cranking event is performed using the standard starting system described. All subsequent ESS engine cranking events are performed by the eTorque system using the Motor Generator Unit. 

IMPORTANT RELAY NAMING INFORMATION: 

The explanation below explains the functionality of the relays and how the Powertrain Control Module (PCM) diagnostics are calibrated to view these relays when displaying faults. When diagnosing a battery/starting/charging system issue there can be confusion on the relay naming when referencing the PDC cover and wiring information due to some of the starting system relay names varying between platforms.

• The first relay in series is controlled by the BCM, but is always considered to be starter relay 2 in the PCM diagnostic calibrations.  When diagnosing any failure mode or PCM DTC  referenced as starter relay 2  , diagnostics should be focused on the relay that is controlled by the BCM  .
• The second relay in series is controlled by the PCM and is always considered to be starter relay 1 in the PCM diagnostic calibrations.  When diagnosing any failure mode or PCM DTC  referenced as starter relay 1  , diagnostics should be focused on the relay that is controlled by the PCM  .

NORMAL OPERATION: 

The initial engine cranking event  occurs when the KIN button is pressed and the engine crank request is sent to the RF Hub.

• The RFH receives the request from the KIN and then looks for the valid key fob by using the LF antennas.
• If the RFH detects a valid key fob and the brake is engaged, the RFH sends a START/CRANK message on the Controller Area Network (CAN).
• If the PCM determines that a crank event is allowed, a CRANK HOLD signal is sent to the BCM.
• The BCM completes the relay coil circuit and energizes starter relay 2.
• The PCM completes the relay coil circuit and energizes starter relay 1, engaging the starter motor.
• After the engine starts (engine speed above a calibrated threshold), the PCM turns off starter relay 1 and the starter is disengaged. The starter is disengaged if the engine does not start after 10 seconds. The ignition state is changed to RUN.

• Transponder backup mode starting:  There is a LF coil located in the KIN that can communicate with the key fobs transponder in close range if the fob battery is dead and complete the authentication. In the event of a key fob issue, push the front edge of the key fob against the start button and hold it there for a few seconds to start the vehicle.
• Emergency shutoff:  The engine can be manually shut down by the driver with speeds over 5 mph (8 km/h) in any gear.

  Courtesy of CHRYSLER GROUP, LLC

  1 - Key Fob

LISTED BELOW ARE OTHER SYSTEMS AND COMPONENTS THAT CONTRIBUTE TO ENGINE STARTING SYSTEM FUNCTIONALITY