For 1990-2009 cars

### Circuit Description

The HVAC control module monitors the outside air quality via the air quality sensor assembly while in AUTO mode. The air quality sensor is a 5-wire sensor, 1 ignition voltage circuit, 2 ground circuits and 2 control circuits. There are 2 sensors inside the air quality sensor assembly. A hydro carbon (HC) sensor which is used for detecting gasoline exhaust fumes and a NOX sensor which is used for detecting nitrous oxide, diesel exhaust fumes. When high levels of hydro carbons (HC) are detected at the front of the vehicle the HC sensor resistance and signal voltage are low. When high levels of NOX are detected at the front of the vehicle the NOX sensor resistance and signal voltage are high.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC B2496 Nox Sensor Circuit (Outside Air Quality Sensor 2 Circuit)

• | DTC B3843 Hydro Carbon Sensor Circuit (Outside Air Quality Sensor 1 Circuit)

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom | DTC Symptom Descriptor
--- | ---
02 | A short to ground

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

The HVAC control module detects the air quality sensor signal circuit is less than 0.09 volt (5 counts).

### Action Taken When the DTC Sets

The driver information center (DIC) will display SERVICE A/C SYSTEM.

### 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 50 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.

1. Tests for the proper operation of the circuit in the low voltage range.

2. Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.

3. Tests for a short to voltage in the 5-volt reference circuit.

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 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, observe the DTC set.

Does the scan tool indicate that DTC B2496 and or B3843 are set?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn OFF the ignition.
2. Unplug the Air Quality Sensor.
3. Turn ON the ignition, with the engine OFF.
4. With a volt meter inspect the air quality NOX sensor signal circuit and the air quality HC sensor signal circuit at the Air Quality Sensor connector.

Does the volt meter display near the specified value on both circuits?

5 V

Go to Step 5

Go to Step 4

4 | Test the appropriate 5-volt sensor signal circuit of the Air Quality Sensor for short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 6
5 | Inspect for poor connections at the harness connector of the Air Quality Sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7
6 | 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 9 | Go to Step 8
7 | Replace the Air Quality Sensor. Refer to Outside Air Quality Sensor Replacement . Have you finished the replacement? | -- | Go to Step 9 | --
8 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Have you finished the replacement? | -- | Go to Step 9 | --
9 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK