Circuit Description
The HVAC control module monitors the outside air quality via the air quality sensor assembly while in AUTO mode. The air quality sensor is a 5-wire sensor, 1 ignition voltage circuit, 2 ground circuits and 2 control circuits. There are 2 sensors inside the air quality sensor assembly. A hydro carbon (HC) sensor which is used for detecting gasoline exhaust fumes and a Nox sensor which is used for detecting nitrous oxide, diesel exhaust fumes. When high levels of hydro carbons (HC) are detected at the front of the vehicle the HC sensor resistance and signal voltage are low. When high levels of Nox are detected at the front of the vehicle the Nox sensor resistance and signal voltage are high.
DTC Descriptors
This diagnostic procedure supports the following DTCs
- DTC B2496 Nox Sensor Circuit (Outside Air Quality Sensor 2 Circuit)
- DTC B3843 Hydro Carbon Sensor Circuit (Outside Air Quality Sensor 1 Circuit)
This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.
| DTC Symptom | DTC Symptom Descriptor |
|---|---|
| 02 | Short to Ground |
DTC B2496 or B3843
Conditions for Running the DTC
The ignition is turned ON.
Conditions for Setting the DTC
The HVAC control module detects the air quality sensor signal circuit is less than 0.09 volt (5 counts).
Action Taken When the DTC Sets
The driver information center (DIC) will display SERVICE A/C SYSTEM.
Conditions for Clearing the DTC
- The DTC will become history if the HVAC control module no longer detects a failure.
- The history DTC will clear after 50 fault-free ignition cycles.
- The DTC can be cleared with a scan tool.
Diagnostic Aids
If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 3: Tests for the proper operation of the circuit in the low voltage range.
- 4: Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
- 5: Tests for a short to voltage in the 5-volt reference circuit.
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | ||||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | |
| 2 | Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, observe the DTC set. Does the scan tool indicate that DTC B2496 and or B3843 are set? | Go to Step 3 | Go to Diagnostic Aids | |
| 3 | Turn OFF the ignition. Unplug the Air Quality Sensor. Turn ON the ignition, with the engine OFF. With a volt meter inspect the air quality Nox sensor signal circuit and the air quality HC sensor signal circuit at the Air Quality Sensor connector. Does the volt meter display near the specified value on both circuits? | 5 V | Go to Step 5 | Go to Step 4 |
| 4 | Test the appropriate 5-volt sensor signal circuit of the Air Quality Sensor for short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 6 | |
| 5 | Inspect for poor connections at the harness connector of the Air Quality Sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 7 | |
| 6 | Inspect for poor connections at the harness connector of the HVAC Control Module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 8 | |
| 7 | Replace the Air Quality Sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement . Did you complete the replacement? | Go to Step 9 | ||
| 8 | Replace the HVAC control module. Refer to Control Module References in Vehicle Control Systems for replacement, setup, and programming. Did you complete the replacement? | Go to Step 9 | ||
| 9 | Use the scan tool in order to clear the DTCs. 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 | |
DTC B2496 or B3843
The HVAC control module monitors the evaporator temperature via the evaporator temperature sensor. When the air is cold, the sensor resistance and signal voltage are high. When the air is warm, the sensor resistance and signal voltage are low.
This diagnostic procedure supports the following DTCs
- DTC B3933 Evaporator Temperature Sensor Circuit
- DTC P1531 Air Conditioning (A/C) Evaporator Temperature Sensor Circuit
This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.
| DTC Symptom | DTC Symptom Descriptor |
|---|---|
| 00 | Out of Range Condition |
DTC B3933
The ignition is turned ON.
The HVAC control module detects the evaporator temperature sensor signal circuit is less than 0.09 volt (5 counts) or greater than 4.90 volts (250 counts).
- The driver information center (DIC) will display SERVICE A/C SYSTEM.
- The A/C OFF segment will illuminate on the HVAC control module.
- The A/C compressor will be disabled.
- The DTC will become history if the HVAC control module no longer detects a failure.
- The history DTC will clear after 50 fault-free ignition cycles.
- The DTC can be cleared with a scan tool.
The numbers below refer to the step numbers on the diagnostic table.
- 3: This step tests for the proper operation of the circuit in the high voltage range.
- 4: This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens upon performing this test, the signal circuit has a short to voltage.
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | ||||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | |
| 2 | Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, observe the Evaporator Temp parameter in the Climate Control Panel, Open/Short data list. Does the scan tool indicate that the Evaporator temp parameter is within the specified range? | 0.09-4.90 V | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
| 3 | Turn OFF the ignition. Disconnect the evaporator temperature sensor. Turn ON the ignition, with the engine OFF. With a scan tool, observe the Evaporator Temp parameter. Is the Evaporator Temp parameter greater than the specified value? | 4.90 V | Go to Step 4 | Go to Step 5 |
| 4 | Turn OFF the ignition. Connect a 3-amp fused jumper wire between the signal circuit of the evaporator temperature sensor and the low reference circuit of the evaporator temperature sensor. Turn ON the ignition, with the engine OFF. With a scan tool, observe the Evaporator Temp parameter. Is the Evaporator Temp parameter less than the specified value? | 0.09 V | Go to Step 9 | Go to Step 6 |
| 5 | Test the signal circuit of the evaporator temperature sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 10 | |
| 6 | Test the signal circuit of the evaporator temperature sensor for one of the following conditions: A short to voltage A high resistance An open Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 7 | |
| 7 | Test the low reference circuit of the evaporator temperature sensor for one of the following conditions: A high resistance An open Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 8 | |
| 8 | Test the following signal circuits for a short to voltage: Inside air temperature sensor Ambient air temperature sensor Left sunload sensor Right sunload sensor Ambient light sensor Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 10 | |
| 9 | Inspect for poor connections at the harness connector of the evaporator temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 11 | |
| 10 | Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 | |
| 11 | Replace the evaporator temperature sensor. Refer to Evaporator Core Replacement in Heating, Ventilation and Air Conditioning. Did you complete the replacement? | Go to Step 13 | ||
| 12 | Replace the HVAC control module. Refer to HVAC Control Module Replacement in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | Go to Step 13 | ||
| 13 | Use the scan tool in order to clear the DTCs. Operate the vehicle within the Conditions for Running the DTC. Does the DTC reset? | Go to Step 2 | System OK | |
DTC B3933
The engine control module (ECM) monitors the high side refrigerant pressure via the A/C refrigerant pressure sensor. The ECM applies a 5-volt reference and a low reference to the sensor. Changes in the A/C refrigerant pressure cause the A/C refrigerant pressure sensor signal to the ECM to vary. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is high the ECM commands the cooling fans on. When pressure is too high or too low the ECM will not allow the A/C compressor clutch to engage. When the DTC is set, the ECM does not allow the A/C compressor clutch to engage. This is done to protect the compressor.
This diagnostic procedure supports the following DTCs
- DTC P0531 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit
- DTC P0532 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit Low Voltage
- DTC P0533 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit High Voltage
- The engine is running.
- The A/C is requested.