B11FC-12

B11FC-12-BLEND AIR SENSOR SHORT TO BATTERY

For a complete wiring diagram, refer to the Wiring Information.





Theory of Operation

The Mixing Chamber Temperature Sensor is a variable resistor that changes in conjunction with temperature, or otherwise known as a thermistor. The Mixing Chamber Temperature Sensor is located in the HVAC housing. The A/C Heater Module monitors the Mixing Chamber temperature by monitoring the voltage change of the Mixing Chamber Temperature Sensor Signal circuit. If the monitored voltage drops below or rises above a predetermined voltage, a Diagnostic Trouble Code (DTC) will set.

- When Monitored:
With the ignition on.

- Set Condition:
The A/C Heater Module detects greater than 4.8 volts on the Mixing Chamber Temperature Sensor Signal circuit for a period of two seconds or more. If the A/C Heater Module detects a valid voltage, the DTC will change from active to stored and will stay stored for 100 ignition cycles.





Always perform the HVAC Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.

Diagnostic Test

1. CHECK IF THE DTC IS ACTIVE
1. Ignition on, engine not running.
2. With the scan tool, read HVAC DTCs.

Is this DTC active?

Yes

- Go To 2

No

- Go To 6

2. CHECK THE MIXING CHAMBER TEMPERATURE SENSOR
1. Turn the ignition off to the lock position.
2. Disconnect the Mixing Chamber Temperature Sensor harness connector.

NOTE: Due to the small terminal and pin size of the Mixing Chamber Temperature Sensor and harness connector, make sure to not damage the terminals in this process.

3. Connect a jumper wire between the (C128) Mixing Chamber Temperature Sensor Signal circuit and the (C121) Sensor Ground circuit in the Mixing Chamber Temperature Sensor harness connector.
4. Ignition on, engine not running.
5. With the scan tool, read the Mixing Chamber Temperature Sensor voltage.

Is the voltage below 0.2 of a volt?

Yes

- Replace the Mixing Chamber Temperature Sensor..
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Go To 3

3. CHECK THE (C128) MIXING CHAMBER TEMPERATURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE
1. Turn the ignition off to the lock position.
2. Disconnect the jumper wire from the previous step.
3. Disconnect the A/C Heater Module C1 harness connector.
4. Ignition on, engine not running.
5. Measure the voltage of the (C128) Mixing Chamber Temperature Sensor Signal circuit.

Is voltage above 0.2 of a volt?

Yes

- Repair the (C128) Mixing Chamber Temperature Sensor Signal circuit for a short to voltage.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Go To 4

4. CHECK THE (C128) MIXING CHAMBER TEMPERATURE SENSOR SIGNAL CIRCUIT FOR AN OPEN
1. Turn the ignition off to the lock position.
2. Measure the resistance of the (C128) Mixing Chamber Temperature Sensor Signal circuit between the A/C Heater Module C1 harness connector and the Mixing Chamber Temperature Sensor harness connector.

Is the resistance above 1.0 Ohm?

Yes

- Repair the (C128) Mixing Chamber Temperature Sensor Signal circuit for an open.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Go To 5

5. CHECK THE (C121) SENSOR GROUND CIRCUIT FOR AN OPEN
1. Measure the resistance of the (C121) Sensor Ground circuit between the A/C Heater Module C1 harness connector and the Mixing Chamber Temperature Sensor harness connector.

Is the resistance above 1.0 Ohm?

Yes

- Repair the (C121) Sensor Ground circuit for an open.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Replace and program the A/C Heater Module. A/C And Heater Control Module - Installation.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

6. CHECK THE WIRING AND CONNECTORS
1. The conditions necessary to set the DTC are not present at this time.
2. With the scan tool, check the Environmental Data to help identify the conditions in which the DTC was set.
3. Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.
4. Wiggle the wiring and connectors while checking for shorted and open circuits.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Test complete.