For 1990-2009 cars

### Circuit Description

The HVAC control module detects exhaust gas by an Air Quality Sensor (AQS).

### DTC Descriptors

This diagnostic procedure supports the following DTC :

DTC B3843 Outside Air Quality Sensor Input Voltage

### Conditions for Running the DTC

Ignition is ON.

### Conditions for Setting the DTC

• | The AQS feedback voltage is less than 0.05 V.

• | The AQS feedback voltage is greater than 4.79 V.

### Action Taken When the DTC Sets

• | The AQS does not operate function.

• | The AQS LED is OFF.

### Conditions for Clearing the DTC

• | The DTC will become history if the HVAC control module no longer detects a fault.

• | The DTC can be cleared with a scan tool.

• | Disconnecting the HVAC control module battery feed for 10 seconds.

### Diagnostic Aids

The number(s) below refer to the step number(s) on the diagnostic table.

1. Tests voltage of the AQS. The range is 0 to 5 volt.

2. Ignition switch is ON and test voltage of the HVAC control module connector terminal A16 and A9.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
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 AQS value in the Heating and Air Conditioning data list.

Does the scan tool indicate that the power transistor assembly parameter is within the specified range?

0.05-5.0 V

Go to Step 7

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the air pollution sensor (AQS).
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe appropriate AQS data parameter.

Does the scan tool indicate that the appropriate AQS data parameter is greater than the specified value?

5.0 V

Go to Step 4

Go to Step 5

4 |

1. Turn OFF the ignition.
2. Connect a fused jumper wire between the signal circuit of the
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe the appropriate AQS.

Does the scan tool indicate that the AQS data parameter is less than the specified value?

0.05 V

Go to Step 7

Go to Step 6

5 | Test the AQS signal circuit for a short to ground. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8
6 | Test the low reference circuit of the AQS for a high resistance, or an open. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8
7 | Inspect for poor connections at the harness connector of the AQS. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9
8 | Inspect for poor connections at the harness connector of the HVAC module. Did you find and correct the condition? | 5.0V | Go to Step 10 | Go to Step 9
9 | Replace the AQS. Did you complete the replacement? | -- | Go to Step 10 | --
10 |

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