For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
1 | Check the coolant level. Is the coolant level correct? | Go to Step 3 | Go to Step 2
2 | Add coolant as needed. Is the heater operating? | System OK | Go to Step 3
3 |

1. Turn the ignition to ON.
2. Observe the temperature indication screen of the controller.

Does the digit flash on and off?

Go to Step 4

Go to Step 5

4 | Run a self-diagnosis circuit check. Does the display indicate a defect code? | Go to the table for the code that flashes | Go to Step 7
5 | Observe the blower motor operation. Is the blower motor functioning at all? | Go to Step 6 | Go to Blower Motor Inoperative
6 | Use the blower push switch to cycle the blower through its different speeds. Does the motor function at different speeds? | Go to Step 7 | Go to Improper Control Response
7 |

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 9

Go to Step 8

8 |

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

Is the heater operating?

System OK

Go to Step 9

9 | Observe the air mix door (AMD) motor while changing the temperature setting from 18 to 32°C (64 to 90°F) and then from 32 to 18°C (90 to 64°F). Is the AMD motor functioning properly? | Go to Step 10 | Go to Air Delivery Improper
10 | Check the coolant hoses for leaks or kinks. Are the coolant hoses in good condition? | Go to Step 12 | Go to Step 11
11 | Repair any problem with the coolant hoses. Is the heater operating? | System OK | Go to Step 12
12 | Check the surge tank cap. Is the surge tank cap in good condition? | Go to Step 14 | Go to Step 13
13 | Repair or replace the surge tank cap as needed. Is the heater operating? | System OK | Go to Step 14
14 |

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 16

Go to Step 15

15 |

1. Check for the following:

• | 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

--

16 | Check 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 18 | Go to Step 17
17 | Back flush or replace the heater core. Is the repair complete? | System OK | --
18 | Check the vehicle for cold air leaks at the

• | Dash

• | Heater cases

• | Vents

Are any leaks found?

Go to Step 20

Go to Step 19

19 | Repair any cold air leaks. Is the repair complete? | System OK | --
20 | Check the coolant temperature sensor using the tests in "Code 3 - Coolant Temperature Sensor Error." Is there a problem indicated in the sensor, the sensor wiring, or the controller? | Go to Step 21 | Go to Step 22
21 | Repair or replace the sensor, the wiring, or the controller as required. Is the repair complete? | System OK | --
22 | Check the in-car sensor using the tests in "Code 1 - In-Car Sensor Error." Is there a problem indicated in the sensor, the sensor wiring, or the controller? | Go to Step 23 | Go to Step 24
23 | Repair or replace the sensor, the wiring, or the controller as required. Is the repair complete? | System OK | --
24 | Check the ambient air temperature sensor using the tests in "Code 2 - Ambient Air Temperature Sensor Error." Is there a problem indicated in the sensor, the sensor wiring, or the controller? | Go to Step 25 | Go to Step 26
25 | Repair or replace the sensor, the wiring, or the controller as required. Is the repair complete? | System OK | --
26 | Check the sun sensor using the tests in "Code 5 - Sun Sensor Error." Is there a problem indicated in the sensor, the sensor wiring, or the controller? | Go to Step 27 | Go to Step 28
27 | Repair or replace the sensor, the wiring, or the controller as required. Is the repair complete? | System OK | --
28 | Replace the ATC controller. Is the repair complete? | System OK | --