Circuit Description
The HVAC control module monitors air temperature through air temperature sensors. When the air is cold, the sensor resistance and signal voltage are high. When the air is warm, the sensor resistance and signal voltage are low. The HVAC control module requests A/C compressor clutch engagement and controls the appropriate mode and air temperature actuator door positions in order to maintain the selected air temperature on the HVAC control module.
The inside air temperature sensor is contained within the HVAC control module. The replacement of the inside air temperature sensor involves the replacement of the HVAC control module. The inside air temperature sensor provides the HVAC control module with the temperature of the air drawn through an aspirator from the passenger compartment across a sensor. A reference voltage is supplied to the sensor thermistor and the HVAC control module determines the voltage drop across that device which is proportional to temperature. As the air temperature increases, the resistance decreases and the voltage signal decreases. As the air temperature decreases, the resistance increases and the voltage signal increases.
Output air temperature sensor 1 circuit refers to the A/C upper duct air temperature sensor.
Output air temperature sensor 2 circuit refers to the heater lower duct air temperature sensor.
Passenger compartment temperature sensor 1 circuit refers to the inside air temperature sensor.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC B0164 Passenger Compartment Temperature Sensor Circuit Range/Performance |
| • | DTC B0174 Output Air Temperature Sensor 1 Circuit |
| • | DTC B0179 Output Air Temperature Sensor 2 Circuit |
This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .
The HVAC control module monitors the signal circuit of the appropriate duct or inside air temperature sensor for the following conditions:
DTC Symptom | DTC Symptom Descriptor |
|---|---|
05 | Short to Battery or Open |
06 | Short to Ground or Open |
Conditions for Running the DTC
The ignition is turned ON.
Conditions for Setting the DTC
B0164 05 and 06
The HVAC control module detects the inside air temperature sensor signal circuit is less than 2 counts or greater than 253 counts for 30 seconds.
B0174 or B0179 05 and 06
The HVAC control module detects the signal circuit is less than 5 counts (0.09 volts) or greater than 250 counts (4.90 volts).
Action Taken When the DTC Sets
B0164 05 and 06
If the DTC sets due to the low condition, the HVAC control module will default to maximum cooling, except when the maximum heating setting is selected. If the DTC sets due to the high condition, the HVAC control module will default to maximum heating, except when the maximum cooling setting is selected.
B0174 or B0179 05 and 06
A default value will be used for the sensor data by the HVAC control module.
Conditions for Clearing the DTC
| • | The DTC will become history if the HVAC control module no longer detects a failure. |
| • | The history DTC will clear after 40 fault-free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Diagnostic Aids
If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for the proper operation of the circuit in the high voltage range.
-
This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate the DTC is current? | -- | Go to Step 6 | Go to Step 3 |
3 |
Does the scan tool indicate that the Sensor parameter is within the specified range? | 5-250 counts (0.09-4.90 V) | Go to Diagnostic Aids | Go to Step 4 |
Does the scan tool indicate that the Sensor parameter is greater than the specified value? | 250 counts (4.90 V) | Go to Step 5 | Go to Step 8 | |
Does the scan tool indicate that the Sensor parameter is less than the specified value? | 5 counts (0.09 V) | Go to Step 11 | Go to Step 9 | |
6 | Test the ignition 3 voltage circuit of the HVAC control module for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 7 |
7 | Test the ground circuit of the HVAC control module for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 |
8 | Test the signal circuit of the appropriate duct air temperature sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 |
9 | Test the signal circuit of the appropriate duct air temperature sensor for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 10 |
10 | Test the low reference circuit of the appropriate duct air temperature sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 11 |
11 | Inspect for poor connections at the harness connector of the appropriate duct air temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 |
12 | Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 |
13 | Replace the upper or lower duct air temperature sensor. Refer to Duct Air Temperature Sensor Replacement - Upper or Duct Air Temperature Sensor Replacement - Lower . Did you complete the replacement? | -- | Go to Step 15 | -- |
14 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | -- |
15 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
