Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual in HVAC Systems - Manual or Symptoms - HVAC Systems - Automatic in HVAC Systems - Automatic

1. Sit inside the vehicle.
2. Close all of the doors and windows.
3. Start the engine.
4. Allow the engine to idle at normal operating temperature.
5. Select the maximum blower speed.
6. Select the VENT 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 3

Go to Step 8

Inspect the HVAC air inlet grille for debris.

Is debris present?

Go to Step 4

Go to Step 5

Remove any debris.

Is the action complete?

Go to Step 15

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Inspect for wet carpeting.

Is the carpet wet?

Go to Step 6

Go to Step 14

Inspect for the following conditions:

Is a leak present?

Go to Step 7

Go to Step 14

Repair the leak as necessary.

Is the repair complete?

Go to Step 15

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Does the odor have a coolant smell?

Go to Step 9

Go to Step 12

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

Is a leak present in the engine compartment?

Go to Step 10

Go to Step 12

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

Is the condition present?

Go to Step 11

Go to Step 15

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 15

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Does the odor have an oily smell?

Go to Step 13

Go to Step 15

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

•	Oil Leak Diagnosis in Engine Mechanical - 4.3L

•	Oil Leak Diagnosis in Engine Mechanical - 4.8L, 5.3L, and 6.0L

•	Oil Leak Diagnosis in Engine Mechanical - 6.6L

•	Oil Leak Diagnosis in Engine Mechanical - 8.1L

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

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

•	Fluid Leak Diagnosis in Automatic Transmission - Allison

•	Power Steering Fluid Leaks in Power Steering System

2. Repair any oil leaks.

Is the repair complete?

Go to Step 15

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A musty odor can be caused by mold or mildew build-up on the evaporator or the heater core or inside of the HVAC module. Refer to Odor Correction .

Is the action complete?

Go to Step 15

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Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2