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 Descriptors
DTC B3843 02
- Air Quality Sensor Circuit Short to Ground
DTC B3843 05
- Air Quality Sensor Circuit High Voltage/Open
DTC B3843 08
- Air Quality Sensor Circuit Performance - Signal Invalid
Diagnostic Fault Information
Circuit/System Description
The HVAC control module uses an air quality sensor to detect hydrocarbons. This sensor operates using an ignition voltage circuit, a ground circuit and a signal circuit.
This information is sent to the HVAC control module using a pulse width modulated (PWM) signal. It is used only when the automatic HVAC mode is requested by the customer.
When the HVAC module detects the concentration of hydrocarbons exceeds a preset value, recirculation mode is commanded to keep the passenger compartment free of pollutants.
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.
Diagnostic Aids
When the conditions that caused the DTC are present, the scan tool Air Quality Sensor parameter will display a constant 100%.
Reference Information
Schematic Reference
HVAC Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
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 Control Module References for scan tool information
Circuit/System Testing
1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the B108 air quality sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal 2 and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
3. Ignition ON.
4. Verify a test lamp illuminates between the ignition circuit terminal 1 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 ohms in the ignition circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the ignition circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the B108 air quality sensor.
• If the test lamp illuminates
5. Install a 3 A fused jumper wire at the signal circuit terminal 3.
6. Verify the scan tool Air Quality Sensor parameter changes while rapidly tapping the fused jumper wire to ground.
• If the parameter does not change
1. Ignition OFF, disconnect the harness connector at the K33 HVAC control module, ignition ON.
2. Test for less than 1 V between the signal circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V
3. Ignition OFF
4. Test for infinite resistance between the signal circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
5. Test for less than 2 ohms in the signal circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K33 HVAC control module.
• If the parameter does change
7. Replace the B108 air quality sensor.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* HVAC Component Replacement Reference Removal and Replacement
* Control Module References Control Module References for HVAC control module replacement, programming, and setup