1. Sit inside the vehicle.
2. Close all of the doors and windows.
3. Start the engine.
4. Allow the engine idle at normal operating temperature.
5. Select the maximum blower speed.
6. Select the panel air outlet mode.
7. Select the coldest temperature setting.
8. Cycle through all of the blower speeds, modes and temperatures 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 7

Inspect for wet carpeting.

Is the carpet wet?

Go to Step 3

Go to Step 12

Inspect for the following conditions:

1. Water leaks around the windshield
2. Blockage of the HVAC module drain
3. Leaks around the door seals

Is a leak present?

Go to Step 4

Go to Step 12

Repair the leak as necessary.

Is the repair complete?

Go to Step 13

--

Does the odor have a coolant smell?

Go to Step 6

Go to Step 10

Inspect the cooling system for leaks. Refer to Cooling System Leak Testing in Engine Cooling.

Is a leak present in the engine compartment?

Go to Step 7

Go to Step 8

Repair the coolant leak as necessary.

Is the repair complete?

Go to Step 13

--

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

Is the condition present?

Go to Step 9

Go to Step 13

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 13

--

Does the odor have an oily smell?

Go to Step 11

Go to Step 13

1. Inspect the engine compartment for any leaks. Refer to the following procedures:

•	Oil Leak Diagnosis 8.1L in Engine Mechanical

•	Fluid Leak Diagnosis in Automatic Transmission - 4L80-E 4L85-E

•	Power Steering Fluid Leaks in Power Steering System

2. Repair any oil leaks.

Is the repair complete?

Go to Step 13

--

A musty odor can be caused by mold or mildew build up on the heater core or inside of the HVAC module.

Is the action complete?

Go to Step 13

--

Operate the system in order to verify the repair.

Is the repair complete?

System OK

Go to Step 1