For 1990-2009 cars

Step | Action | 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
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, observe the IPM Air Quality Sensitivity setting in the HVAC IPM Special Functions List.

Does the scan tool indicate that a lower air quality number can be selected to increase the sensitivity level of the air quality sensor?

Go to Step 3

Go to Step 4

3 | Adjust the sensitivity level to increase the sensitivity of the air quality sensor. Refer to Air Quality Calibration Offset . Operate the system in order to verify the condition. Did you correct the condition? | Go to Step 17 | Go to Step 4
4 |

1. Turn OFF the ignition.
2. Unplug the Air Quality Sensor.
3. Turn ON the ignition, with the engine OFF.
4. Turn ON the HVAC module.
5. With a test lamp connected to battery voltage probe the ground circuit at the Air Quality Sensor connector.

Does the test lamp illuminate?

Go to Step 5

Go to Step 12

5 | With a test lamp connected to battery voltage probe the low reference circuit at the Air Quality Sensor connector. Does the test lamp illuminate? | Go to Step 6 | Go to Step 13
6 | With a test lamp connected to ground probe the ignition 1 voltage circuit at the Air Quality Sensor connector. Does the test lamp illuminate? | Go to Step 7 | Go to Step 14
7 | 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 5 volts or greater on either circuit? | Go to Step 8 | Go to Step 9
8 | Test the appropriate 5-volt sensor signal circuit of the Air Quality Sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 17 | Go to Step 10
9 | Test the appropriate 5-volt sensor signal circuit of the Air Quality Sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 17 | Go to Step 11
10 | 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 . Did you find and correct the condition? | Go to Step 17 | Go to Step 15
11 | 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 . Did you find and correct the condition? | Go to Step 17 | Go to Step 15
12 | Repair the ground circuit of the Air Quality Sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 17 | --
13 | Repair the low reference circuit of the Air Quality Sensor for an open, high resistance or short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 17 | --
14 | Repair the ignition 1 voltage circuit of the Air Quality Sensor for an open, high resistance or short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 17 | --
15 | Replace the Air Quality Sensor. Have you finished the replacement? | Go to Step 17 | --
16 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Have you finished the replacement? | Go to Step 17 | --
17 | Operate the system in order to verify the repair. Did you correct the condition? | Go to Step 2 | System OK