Theory Of Operation

WARNING: This page is about a different car, the 2017 Jeep Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

The Engine Stop/Start (ESS) system uses an In-Rush Current Relay (ICR) to reduce the voltage drop during an AutoStart event. The purpose of this is for the consumer electronics and vehicle subsystems to continue to function in a normal manner. The ICR is connected in-line of the main Battery feed to the Starter Motor. The ICR energizes when 12 volts is supplied to the coil by the In-Rush Current (ICR) Control Relay, which is controlled by the Powertrain Control Module (PCM).

The ICR is normally closed in the off position. This means that when it is de-energized, the relay is closed and full Battery current is allowed to pass through the ICR directly to the Starter Motor with no resistance. During all key crank events the ICR is in this mode of operation and voltage drop is approximately 3.5 volts during cranking.

However, during an AutoStart crank event in ESS mode , the ICR is energized which opens the relay. When this occurs, Battery current to the Starter Motor is diverted through the resistor inside the ICR and then to the Starter Motor. Once the Starter Motor has engaged, the ICR is turned off allowing full Battery current to flow to the Starter Motor. This reduces the voltage drop approximately 2.0 volts during an Auto Start cranking event.