Theory Of Operation - Relays

In diesel applications there are three Positive Temperature Coefficient (PTC) Relays, located in the Power Distribution Center (PDC) Assembly, are used for the PTC Cabin Heater System. The PTC Relays are used to supply fused battery voltage directly to the heating elements of the Cabin Heater. When the Body Control Module (BCM) receives a PTC Cabin Heater System activation CAN Bus message from the Powertrain Control Module (PCM), the BCM provides a ground signal, through the PTC Relay Control circuits, to activate the PTC Relays. When the PTC Relays are activated, a voltage output is sent to the Cabin Heater through the Fused Cabin Heater Supply circuits.