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 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 filter for debris.

Is the HVAC filter clean of debris?

Go to Step 5

Go to Step 4

Remove any debris from the filter.

Is the action complete?

Go to Step 16

--

Inspect for wet carpeting.

Is the carpet wet?

Go to Step 6

Go to Step 15

Inspect for the following conditions:

Is a leak present?

Go to Step 7

Go to Step 15

Repair the leak as necessary.

Is the repair complete?

Go to Step 16

--

Does the odor have a coolant smell?

Go to Step 9

Go to Step 13

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 11

Repair the coolant leak as necessary.

Is the repair complete?

Go to Step 16

--

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

Is the condition present?

Go to Step 12

Go to Step 16

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 16

--

Does the odor have an oily smell?

Go to Step 14

Go to Step 16

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 16

--

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 16

--

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2