1. Turn OFF the engine.
2. Ensure that the engine temperature is cool.
3. Check 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

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

Are the inlet and the outlet hoses 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. Refer to Cooling System Leak Testing in Engine Cooling.
2. Fill the coolant system.
3. Bleed the air from the coolant system. Refer to Cooling System Draining and Filling in 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.

Refer to Flushing in Engine Cooling or Heater Core Replacement .

Is the repair complete?

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System OK

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