Circuit Description
The following DTCs are for the auxiliary air temperature sensors located in the auxiliary HVAC ducts:
| • | B3579 is for the upper auxiliary air temperature sensor. |
| • | B3584 is for the lower auxiliary air temperature sensor. |
The auxiliary air temperature sensors allow the auxiliary HVAC control module to monitor the temperature of the discharge air in the auxiliary HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The auxiliary HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The auxiliary HVAC control module converts the voltage values to count values where 1 V is approximately equal to 51 counts.
Conditions for Running the DTC
| • | Battery voltage is within 8.7-16.5 V. |
| • | The ignition is ON. |
Conditions for Setting the DTC
The auxiliary HVAC control module determines that the value of the air temperature parameter is less than 5 counts or greater than 250 counts.
Action Taken When the DTC Sets
The auxiliary HVAC control module uses a default air temperature value for further automatic control calculations. The default values are displayed on the scan tool. The default value is 50 Counts.
Conditions for Clearing the DTC
| • | The DTC will become history if the auxiliary HVAC control module no longer detects a fault. |
| • | The history DTC will clear after 100 fault-free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
Does the scan tool indicate that B3579 or B3584 is a current DTC? | -- | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | |
3 |
Does the voltage measure near the specified value? | 5 V | Go to Step 4 | Go to Step 5 |
4 | Measure the voltage from the signal circuit to the low reference circuit of the auxiliary air temperature sensor. Does the voltage measure near the specified value? | 5 V | Go to Step 7 | Go to Step 6 |
5 | Test the signal circuit of the appropriate auxiliary air temperature sensor for an open, high resistance, short to ground, or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 |
6 | Test the low reference circuit of the appropriate auxiliary air temperature sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 |
7 | Inspect for poor connections at the harness connector of the appropriate auxiliary air temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9 |
8 | Inspect for poor connections at the harness connector of the auxiliary HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the appropriate auxiliary air temperature sensor. Refer to one of the following procedures: Did you complete the replacement? | -- | Go to Step 11 | -- |
10 | Replace the auxiliary HVAC control module. Refer to Auxiliary Heater and Air Conditioning Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
11 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
