Orlando

DTC B3843

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.

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.

The automatic recirculation mode is disabled.

The condition for setting the DTC is no longer present.

Schematic Reference

HVAC Schematics : Automatic

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Verify that DTC B3843 08 is not set.

⇒	If DTC B3843 08 is present

Replace the B108 Air Quality Sensor.

⇓	If DTC B3843 08 is not present

2. Verify that DTC B3843 02 or B3843 05 is not set.

⇒	If DTC B3843 02 or B3843 05 is present

Refer to Circuit/System Testing.

⇓	If DTC B3843 02 and B3843 05 are not present

3. All OK.

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 5 Ω

Repair the open/high resistance in the circuit.

⇓	If less than 5 Ω

3. Ignition ON, verify that 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

3.1.	Ignition OFF.

3.2.	Test for less than 2 Ω in the ignition circuit end to end.

⇒	If 2 Ω or greater, repair the open/high resistance in the circuit.

⇒	If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

⇒	If the test lamp does not illuminate and the circuit fuse is open

3.1.	Ignition OFF.

3.2.	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

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

⇒	If less than 95%

4.1.	Ignition OFF, disconnect the X1 harness connector at the K33 HVAC Control Module.

4.2.	Ignition ON, test for infinite resistance between the signal circuit terminal 3 and ground.

⇒	If less than infinite resistance, repair the short to ground on the circuit.

⇒	If infinite resistance, replace the K33 HVAC Control Module.

⇓	If greater than 95%

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

⇒	If greater than 5%

5.1.	Ignition OFF, disconnect the X1 harness connector at the K33 HVAC Control Module.

5.2.	Ignition ON, test for less than 0.3 V between the signal circuit and ground.

⇒	If greater than 0.3 V, repair the short to voltage on the circuit.

⇓	If less than 0.3 V

5.3.	Ignition OFF, test for less than 2 Ω in the signal circuit end to end.

⇒	If 2 Ω or greater, repair the open/high resistance in the circuit.

⇒	If less than 2 Ω, replace the K33 HVAC Control Module

⇓	If less than 5%

6. Replace the B108 Air Quality Sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.