1. Sit inside the vehicle.
2. Close all doors and windows.
3. Start the engine .
4. Let the engine idle at normal operating temperature.
5. Set the blower speed to HI.
6. Set the mode to VENT.
7. Set the temperature control to full COLD.
8. Cycle through all blower speeds, modes and temperature control positions to define what type of odor is present.

•	Musty smell

•	Coolant smell

•

Oil smell

Does the odor have a musty smell?

Go to Step 2

Go to Step 5

1. Inspect the evaporator drain tube for a blockage.
2. Clean and repair the blockage as necessary.

Was the drain plugged and an excessive amount of water present?

Go to Step 3

Go to Step 4

1. Inspect for a water leak at the plenum to windshield seal.
2. Inspect the HVAC filter cover and for debris on the filter.
3. Inspect for wet carpet or mats and the HVAC case seals at the front of dash.
4. Repair the leak as necessary.

Did you complete the repair?

Go to Step 13

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The probable odor is caused by mold/mildew build up within the HVAC case and on the evaporator and heater cores. To correct the odor refer to Odor Correction .

Did you complete the repair?

Go to Step 13

--

Does the odor have a coolant smell?

Go to Step 6

Go to Step 11

Inspect the cooling system for leaks. Refer to Loss of Coolant in Engine Cooling.

Is their a leak present in the engine compartment area?

Go to Step 7

Go to Step 8

Repair the leak as necessary.

Did you complete the repair?

Go to Step 13

--

Inspect for coolant leaking inside the vehicle and/or a film build up on the windshield.

Is there a leak present?

Go to Step 9

Go to Step 11

Replace the heater core. Refer to Heater Core Replacement .

Did you complete the repair?

Go to Step 13

--

1. Verify the complaint.
2. It is possible to have a leak in the heater core without a visual leak outside of the case.
3. Remove the heater core and visually inspect for a leak. Refer to Heater Core Replacement .
4. Repair as necessary.

Did you complete the repair?

Go to Step 13

--

Does the odor have an oil smell?

Go to Step 12

System OK

1. Inspect the engine compartment area for an oil leak. Refer to the following for leak diagnosis:

•	Oil Leak Diagnosis in Engine Mechanical - 4.3L

•	Oil Leak Diagnosis in Engine Mechanical - 5.0L and 5.7L

•	Oil Leak Diagnosis in Engine Mechanical - 6.5L

•	Oil Leak Diagnosis in Engine Mechanical - 8.1L

•	Fluid Leak Diagnosis in Automatic Transmission - 4L60-E

•	Fluid Leak Diagnosis in Automatic Transmission - 4L80-E

•	Power Steering Fluid Leaks in Power Steering

2. Repair any oil leaks.

Did you complete the repair?

Go to Step 13

--

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 1