GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 XLR 🢒 HVAC 🢒 HVAC - Automatic 🢒 Heating Performance Diagnostic

Step

Action

Yes

No

DEFINITION: Heating system performance.

1

Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Symptoms - HVAC Systems - Automatic

2
  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

3

    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 near the heater core.

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

Go to Step 7

Go to Step 4

4
  1. Install a thermometer into the center I/P 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:
    7. • The center I/P 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

5
  1. Inspect and repair the following areas of the vehicle for cold air leaks:
    2. • The cowl
    • The recirculation door
    • The HVAC module case
  2. Perform the necessary repairs.

Are the repairs complete?

Go to Step 10

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6
  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

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7
  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 near the heater core.

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

Go to Step 8

Go to Step 10

8

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 10

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9

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

Is the repair complete?

Go to Step 10

--

10

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2