DEFINITION: Heating system performance.

Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

or

Go to Symptoms - HVAC Systems - Automatic

1. Start the engine.
2. Allow the engine to idle.

Does the engine reach a normal operating temperature?

Go to Step 3

Go to Step 9

Caution: Refer to Moving Parts and Hot Surfaces Caution in the Preface section.

1. Allow the engine to idle.
2. Select the FLOOR mode.
3. Select the minimum blower speed.
4. Select the warmest temperature setting.
5. Feel the temperature of the inlet and outlet heater hoses at the heater core.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 7

Go to Step 4

1. Install a thermometer into the center IP PANEL air outlet.
2. Secure a thermometer to the heater core outlet hose.
3. Select the PANEL mode.
4. Select the maximum blower speed.
5. Select the warmest temperature setting.
6. Record the temperature at the following locations:

•	The center IP PANEL air outlet

•	The heater core outlet hose

7. Compare the recorded temperatures.

Are the two temperature readings about equal?

Go to Step 5

Go to Step 6

1. Inspect and repair the following areas of the vehicle for cold air leaks:

•

The cowl

•	The recirculation door

•	The HVAC module case

2. Perform the necessary repairs.

Are the repairs complete?

Go to Step 10

--

1. Inspect the temperature door operation. Refer to Diagnostic System Check - Vehicle .
2. Perform any necessary repairs.

Are the repairs complete?

Go to Step 10

--

1. Turn OFF the engine.
2. Backflush the heater core.
3. Start the engine.
4. Select the FLOOR mode.
5. Select the minimum blower speed.
6. Select the warmest temperature setting.
7. Feel the temperature of the inlet and outlet heater hoses at the heater core.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 8

Go to Step 10

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 10

--

Repair the low engine temperature concern. Refer to Engine Fails To Reach Normal Operating Temperature .

Is the repair complete?

Go to Step 10

--

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2

DEFINITION: Heating system performance of the auxiliary heater

Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Air Temperature Malfunction .

1. Start the engine.
2. Allow the engine to idle.

Does the engine reach a normal operating temperature?

Go to Step 3

Go to Step 9

Caution: Refer to Moving Parts and Hot Surfaces Caution in the Preface section.

1. Allow the engine to idle.
2. Select the warmest auxiliary temperature setting.
3. Select the minimum auxiliary blower speed.
4. Feel the temperature of the inlet and outlet auxiliary heater hoses.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 7

Go to Step 4

1. Install a thermometer into an auxiliary air outlet.
2. Secure a thermometer on the outlet heater hose of the auxiliary heater core.
3. Select the maximum auxiliary blower speed.
4. Select the warmest auxiliary temperature setting.
5. Record the temperature at the following locations:

•	The auxiliary air outlet

•	The auxiliary heater core outlet hose

6. Compare the recorded temperatures.

Are the 2 temperature readings about equal?

Go to Step 5

Go to Step 6

1. Inspect the following areas of the vehicle for cold air leaks:

•	The auxiliary HVAC module case

•	The auxiliary air ducts

2. Perform any necessary repairs.

Is the repair complete?

Go to Step 11

--

Inspect the auxiliary HVAC module for correct temperature door operation.

Does the temperature door operate correctly?

Go to Step 11

Go to Step 10

1. Turn OFF the engine.
2. Backflush the auxiliary heater core.
3. Start the engine and allow the engine to idle.
4. Select the minimum auxiliary blower speed.
5. Select the warmest auxiliary temperature setting.
6. Feel the temperature of the inlet and outlet heater hoses at the auxiliary heater core.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 8

Go to Step 11

Replace the auxiliary heater core. Refer to Auxiliary Heater Core Replacement .

Is the repair complete?

Go to Step 11

--

Repair the low engine temperature concern. Refer to Engine Fails To Reach Normal Operating Temperature .

Is the repair complete?

Go to Step 11

--

Repair the temperature door operation.

Is the repair complete?

Go to Step 11

--

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2