GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

1

Inspect for a missing or damaged radiator, upper or lower baffle, and/or radiator air deflector.

Is the baffle and/or deflector missing or damaged?

Go to Step 8

Go to Step 2

2

Inspect for a loss of coolant.

Is there a loss of coolant?

Go to Step 3

Go to Step 4

3

Fill the system to the specified level. Refer to Loss of Coolant .

Does the engine overheat?

Go to Step 4

System OK

4

Inspect for low coolant protection.

Is the coolant to the correct concentration?

Go to Step 5

Go to Step 8

5

Inspect for a loss of cooling system pressure.

Is there a loss of system pressure?

Go to Step 8

Go to Step 6

6

Inspect for a faulty engine coolant temperature (ECT) sensor. Refer to DTC P0128 for the 4.4L (LC3) engine, or DTC P0128 for the 4.6L (LH2) engine.

Is the sensor operating properly?

Go to Step 7

Go to Step 8

7

Inspect for a cracked coolant surge tank or a leaking hose.

Is the coolant surge tank cracked or is the hose leaking?

Go to Step 8

Go to Step 3

8

Repair or install new parts as necessary, then retest.

Does the engine overheat?

Go to Step 9

System OK

9

Inspect for incorrect drive belt tension.

Is the belt tension correct?

Go to Step 10

Go to Step 8

10

  1. Remove the water pump. Refer to Water Pump Replacement .
  2. Inspect for a damaged water pump driveshaft.

Is the water pump driveshaft damaged or is the seal leaking?

Go to Step 8

Go to Step 11

11

Inspect for obstructed radiator air flow or bent radiator fins.

Is the radiator air flow obstructed?

Go to Step 8

Go to Step 12

12

Inspect for blocked cooling system passages.

Are the cooling system passages blocked?

Go to Step 8

Go to Step 13

13

Inspect for inoperative cooling fans. Refer to Cooling Fan Inoperative .

Are the cooling fans and the motors operating correctly?

Go to Step 14

Go to Step 8

14

Inspect the thermostat. Refer to Thermostat Diagnosis .

Is the thermostat stuck in the closed position?

Go to Step 15

Go to Step 16

15

Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .

Does the engine overheat?

Go to Step 16

System OK

16

Inspect the radiator cooling capacity.

Is the proper sized radiator being used on the vehicle?

Go to Step 3

Go to Step 17

17

Consult the current parts catalog and replace the radiator. Refer to Radiator Replacement .

Is the repair complete?

System OK

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