Circuit Description
The rear HVAC control module monitors the air temperature in the lower auxiliary discharge duct via a temperature sensor. 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 rear auxiliary HVAC control module converts this voltage to a digital signal that can be transmitted over the keyboard display driver (KDD) data bus to the HVAC control module. The HVAC control module contains the logic that controls the auxiliary air temperature and is responsible for setting the DTC.
Conditions for Running the DTC
The ignition is turned ON.
Conditions for Setting the DTC
The HVAC Control Module - Rear Auxiliary detects the signal circuit is less than 0.09 V (5 counts) or greater than 4.90 V (250 counts).
Action Taken When the DTC Sets
A default value of 2.50 V (127 counts) will be used for the sensor data by the HVAC control module. The sensor reading displayed on the scan tool in the HVAC data list will be this default value.
Conditions for Clearing the DTC
| • | The DTC will become history if the HVAC Control Module - Rear Auxiliary no longer detects a failure. |
| • | The history DTC will clear after 50 fault free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Diagnostic Aids
Check the following conditions:
| • | Visually inspect the sensor for contamination or damage. |
| • | Verify that air flow to sensor is not restricted. |
| • | Verify that the sensor is installed properly. |
| • | Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Air Delivery/Temperature Control Schematics | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check |
2 |
Does the voltage measure near the specified value? | 5 V | Go to Step 3 | Go to Step 4 |
3 | Measure the voltage from the rear heater temperature sensor signal circuit to the low reference circuit of the rear heater temperature sensor. Does the voltage measure near the specified value? | 5 V | Go to Step 6 | Go to Step 5 |
4 | Test the rear heater temperature sensor signal circuit of the rear heater 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 12 | Go to Step 9 |
5 | Test the low reference circuit of the rear heater 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 12 | -- |
6 | Inspect for poor connections at the harness connector of the rear heater 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 12 | Go to Step 7 |
7 | Test the rear heater temperature sensor resistance. Refer to the Sensor Resistance Table . Does the resistance measure near the Sensor Resistance Table value? | -- | Go to Step 8 | Go to Step 10 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | |
9 | Inspect for poor connections at the harness connector of the rear 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 12 | Go to Step 11 |
10 | Replace the rear heater temperature sensor. Refer to Heater Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 |
Important:: Perform the set up procedure for the rear HVAC control module. Replace the rear HVAC control module. Refer to Control Assembly Replacement - Auxiliary . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
