For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic Trouble Code (DTC) List - Vehicle
2 | Inspect the coolant level. Is the coolant level correct? | Go to Step 4 | Go to Step 3
3 | Add coolant as needed. Did you correct the condition? | System OK | --
4 | Observe the blower motor operation. Is the blower motor functioning at all? | Go to Step 5 | Go to Blower Motor Inoperative
5 | Use the blower push switch to cycle the blower through its different speeds. Does the motor function at different speeds? | Go to Step 6 | Go to Blower Motor Inoperative
6 |

1. Run the blower and operate the MODE push switch manually.
2. Check for airflow out the various outlets.

Does the air flow from the different outlets as it should?

Go to Step 8

Go to Step 7

7 |

1. Remove the heater outlet and inspect for obstructions.
2. Remove any obstructions found.

Is the heater operating?

System OK

Go to Step 8

8 | Observe the air mix door (AMD) motor while changing the temperature setting from 18-32°C (64-90°F) and then from 32-18°C (90-64°F). Is the AMD motor adjusting to temperature properly? | Go to Step 9 | Go to DTC 4
9 | Inspect the coolant hoses for leaks or kinks. Are the coolant hoses in good condition? | Go to Step 11 | Go to Step 10
10 | Repair any problem with the coolant hoses. Is the heater operating? | System OK | Go to Step 11
11 | Inspect the surge tank cap. Is the surge tank cap in good condition? | Go to Step 13 | Go to Step 12
12 | Repair or replace the surge tank cap as needed. Is the heater operating? | System OK | Go to Step 13
13 |

1. Set the A/C switch to OFF.
2. Set the temperature control to 32°C (90°F).
3. Set the blower motor speed to full high, all segments illuminated on the display.
4. Remove the surge tank cap.
5. Start the vehicle and run the engine at idle.
6. Watch for the flow of the coolant when the thermostat opens.

Does the coolant flow?

Go to Step 15

Go to Step 14

14 |

1. Inspect for the following conditions:

• | A faulty thermostat

• | A failed coolant pump impeller

• | A restriction in the cooling system

2. Make repairs as needed.

Is the repair complete?

System OK

--

15 | Inspect the temperature of the heater inlet and outlet hoses by feel. Is the heater inlet hose hot and the outlet hose warm? | Go to Step 17 | Go to Step 16
16 | Back flush or replace the heater core. Is the repair complete? | System OK | --
17 | Inspect the vehicle for cold air leaks at the following locations:

• | Dash

• | Heater cases

• | Vents

Are any leaks found?

Go to Step 19

Go to Step 18

18 | Repair any cold air leaks. Is the repair complete? | System OK | --
19 | Inspect the coolant temperature sensor. Is there a problem indicated in the sensor, the sensor wiring or the controller? | Go to Step 20 | Go to Step 21
20 | Repair or replace the sensor, the wiring, or the controller as required. Is the repair complete? | System OK | --
21 | Inspect the in-car sensor. Refer to DTC 1 . Is there a problem indicated in the sensor, the sensor wiring, or the controller? | Go to Step 20 | Go to Step 22
22 | Inspect the ambient air temperature sensor. Refer to DTC 2 . Is there a problem indicated in the sensor, the sensor wiring, or the controller? | Go to Step 20 | Go to Step 23
23 | Inspect the sun sensor. Refer to DTC 5 . Is there a problem indicated in the sensor, the sensor wiring, or the controller? | Go to Step 20 | Go to Step 24
24 | Replace the automatic temperature controller (ATC). Refer to Heater and Air Conditioning Control Replacement . Is the repair complete? | System OK | --