B3843

DTC B3843

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC B3843 00
- Outside Air Quality Sensor Circuit Malfunction

DTC B3843 02
- Outside Air Quality Sensor Circuit Short to Ground

DTC B3843 05
- Outside Air Quality Sensor Circuit High Voltage/Open

DTC B3843 21
- Outside Air Quality Sensor Circuit Performance - Signal Invalid

Diagnostic Fault Information





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 sensor outputs a PWM Signal to the HVAC control module with different levels of pollution as detected outside.

The HVAC control module evaluates the information of the air quality sensor and closes the recirculation door 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 00

If the PWM signal is greater than 97% for more than 30 seconds.

B3843 02

No PWM is detected and the signal is low for more than 30 seconds.

B3843 05

No PWM is detected and the signal is high for more than 30 seconds.

B3843 21

PWM signal is detected but the frequency is outside of the valid range for more than 30 seconds.

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 (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Automatic HVAC Description and Operation (HVAC - Automatic)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the Air Quality Sensor.
2. Test for less than 5 ohm 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. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 3 and ground.

• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
• If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.

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

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Ambient Air Quality Sensor Replacement (Ambient Air Quality Sensor Replacement)
* Control Module References (Programming and Relearning) for HVAC Control Module replacement, setup, and programming