B108F

B108F-AUTOMATIC TEMPERATURE CONTROL SYSTEM PERFORMANCE (ATC)


Theory of Operation
The Powertrain Control Module (PCM) transmits Engine Coolant Temperature Sensor data to modules wired to the CAN C bus. The Front Control Module (FCM) in turn transmits the Engine Coolant Temperature Sensor data to modules wired to the CAN B bus. The FCM also transmits Ambient Temperature Sensor data to modules wired to the CAN B bus. The Compass Temperature Module (EOM) transmits Infrared Sensor data to modules wired to the CAN B bus. The A/C Heater Control requires all of this data in order to provide automatic temperature control operation.

WHEN MONITORED
With the ignition on.

SET CONDITION
If the A/C Heater Control either fails to receive Engine Coolant Temperature Sensor data, Ambient Temperature Sensor data, or Infrared Sensor data, or if the data from any of these sensors is out of range. This DTC has a maturing time of 5 seconds and a de-maturing time of 10 seconds. If the DTC's status changes from active to stored it will stay in memory for 100 ignition cycles.

POSSIBLE CAUSES
- Powertrain control module (PCM), front control module (FCM), or compass temperature module (EOM) not active on the BUS
- CAN B BUS circuits open or shorted, CAN C BUS circuits open or shorted, ambient temperature sensor circuits, engine coolant temperature sensor circuits, or infrared sensor circuits shorted or open
- Ambient temperature sensor, engine coolant temperature sensor, or infrared sensor inoperative
- Powertrain control module (PCM), front control module (FCM), or compass temperature module (EOM) failing to transmit data on the BUS
- A/C heater control module failing to receive transmitted data from the BUS

Diagnostic Test

1. VERIFY THAT DTC B108F-AUTOMATIC TEMPERATURE CONTROL SYSTEM PERFORMANCE IS ACTIVE
With the scan tool, read HVAC DTCs.

Q: Is DTC B108F-AUTOMATIC TEMPERATURE CONTROL SYSTEM PERFORMANCE active?

YES: Go To 2
NO: A technician may not have erased this DTC following a module or CAN Bus repair. If possible, verify if the vehicle was recently in for this type of service. Otherwise, visually inspect the related wiring harness for chafed, pierced, pinched, and partially broken wires and the wiring harness connectors for broken, bent, pushed out, and corroded terminals. Repair as necessary.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

2. CHECK FOR ACTIVE DTC U0019-CAN B BUS CIRCUIT
With the scan tool, read active HVAC DTCs.

Q: Does the scan tool display active: U0019-CAN B BUS CIRCUIT?

YES: Diagnose and repair the DTC. Refer to the Trouble Code Diagnostic Charts for a complete list of HVAC symptoms.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 3

3. VERIFY THAT THE PCM, FCM, & EOM are ACTIVE ON THE BUS
Turn the ignition on.
With the scan tool, select ECU View.
Verify that the PCM, FCM, & EOM are active on the bus.

Q: Are all of the modules active on the bus?

YES: Go To 4
NO: Refer to Diagnosis By Symptom for No Response diagnostic procedures. Manufacturer Code Charts
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

4. CHECK FOR DTCs IN THE PCM, FCM, & EOM
With the scan tool, select ECU View.
Check for DTCs in the PCM, FCM, and EOM.

Q: Are DTCs present in any of the modules?

YES: Diagnose and repair the DTC(s).
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Replace the A/C Heater Control.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test