1. Turn the engine OFF.
2. Ensure that the engine temperature is cool.
3. Inspect the coolant level in the radiator and the reservoir.

Is the coolant level low?

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Go to Step 5

Go to Step 2

1. Connect the Scan Tool .
2. Start the engine.
3. Monitor the engine coolant temperature.

Does the coolant temperature increase steadily to the normal operating temperature?

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Go to Step 3

Go to Step 6

Feel the inlet and the outlet hoses of the heater core.

Do both inlet and outlet hoses feel hot?

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Go to Step 4

Go to Step 7

Inspect the heater core for bent fins or other obstructions.

Did you locate and repair an obstruction?

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System OK

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1. Inspect the cooling system for signs of leakage.
2. Fill the coolant system.
3. Bleed the air from the coolant system. Refer to engine cooling.

Did you add coolant to the system?

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System OK

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Replace the faulty thermostat. Refer to Engine Coolant Thermostat Replacement in Engine Cooling.

Is the repair complete?

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System OK

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1. Inspect the hoses for kinks or other obstructions.
2. Flush or replace the obstructed heater core.

Is the repair complete?

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System OK

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