Cabin Heater

When the ignition is in Run, the FCM monitors the PCI bus for the Cabin Heater Activation request. The Automatic or Manual Temperature Control initiates this request only when all conditions for the Cabin Heater activation are favorable. The request carries the status bit that the FCM requires to activate its Cabin Heater Assist Control output. This output is a low side driver (coming from FCM pin 15) which supplies a ground signal to the Cabin Heater (pin 5). When the Cabin Heater receives this ground signal input, it interprets this as an activation signal. The FCM is capable of diagnostic sensing. A cabin relay open is sensed if the output is off and there is a open condition. A cabin relay short to voltage is sensed if the output is active and there is a short to voltage condition. The FCM will set DTCs for both of these types of faults. For additional information, refer to CABIN HEATER  under General Information and Diagnostic Procedures in the service information.