For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC B3843 02: Outside Air Quality Sensor Circuit Short to Ground
DTC B3843 05: Outside Air Quality Sensor Circuit Short to Battery or Open
DTC B3843 08: Outside Air Quality Sensor Circuit Invalid Signal

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Air Quality Sensor Ignition | -- | B3843 05 | -- | --
Air Quality Sensor Signal | B3843 02 | B3843 05 | B3843 05 | B3843 08
Air Quality Sensor Ground | -- | B3843 05 | -- | --

### Circuit/System Description

The HVAC control module detects exhaust gas by an air quality sensor. The air quality sensor is a 3-wire sensor with an ignition voltage circuit, a ground circuit and a signal circuit.

The information is pulse width modulation (PWM) signal generated on the output pin.

The HVAC control module evaluates the information of the air quality sensor and closes the recirculation flap while in the automatic mode, as soon as the concentration of pollutants exceeds a preset value.

### Conditions for Running the DTC

• | Ignition ON.

• | The HVAC control module is ON.

### Conditions for Setting the DTC

#### B3843 02

No PWM is detected and the signal is low.

#### B3843 05

No PWM is detected and the signal is high.

#### B3843 08

The Sensor sends a 5% PWM signal indicating an internal sensor short circuit or open circuit.

### Action Taken When the DTC Sets

The automatic recirculation mode is disabled.

### Conditions for Clearing the DTC

The condition for setting the DTC is no longer present.

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Automatic HVAC Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Verify that DTC B3843 08 is not present.

⇒ | If DTC is present, replace the B108 Air Quality Sensor.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the B108 Air Quality Sensor.
2. Test for less than 5 Ω between the ground circuit terminal 2 and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 and ground.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance.

4. Verify the scan tool Odor Sensor parameter is greater than 95%.

⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the K33 HVAC Control Module.

5. Install a 3 A fused jumper wire between the following signal circuit terminal 3 and the ground circuit terminal 2. Verify the scan tool Odor Sensor parameter is less than 5%.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage or open/high resistance. If the circuit tests normal, replace the K33 HVAC Control Module.

6. If all circuits test normal, replace the B108 Air Quality Sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Ambient Air Quality Sensor Replacement

• | Control Module References for HVAC Control Module replacement, setup, and programming