GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Envoy - 2WD 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Loss of Coolant

Step

Action

Yes

No

DEFINITION: The cooling system is losing coolant either internally or externally.

1

Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Symptoms - Engine Cooling

2

Repair any present DTCs. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

Is the action complete?

Go to Step 3

Symptoms - Engine Cooling

3

Inspect the coolant level.

Is the coolant at the proper level?

Go to Step 5

Go to Step 4

4

Fill the cooling system to the proper level. Refer to Cooling System Draining and Filling .

Is the action complete?

Go to Step 5

--

5

If the engine is suspected to have a coolant leak into the cylinder, the coolant can hydraulically lock the cylinder.

Does the engine crankshaft rotate?

Go to Step 6

Go to Step 30

6

Engine overheating can cause a loss of coolant.

Is the engine overheating?

Go to Step 30

Go to Step 7

7

Extended engine operation with a low coolant level can cause engine internal component failure.

Is the engine knocking?

Go to Step 32

Go to Step 8

8
  1. Idle the engine at normal operating temperature.
  2. Inspect for heavy, white smoke coming out of the exhaust pipe.

Is a heavy, white smoke present from the exhaust pipe?

Go to Step 9

Go to Step 10

9
    • Coolant in the exhaust system creates a distinctive, burning coolant odor in the exhaust.
    • Condensation in the exhaust system can cause an odorless, white smoke during engine warm up.

Does the white smoke have a burning coolant type odor?

Go to Step 31

Go to Step 10

10

With the engine idling, inspect the coolant recovery system.

Does the coolant recovery system discharge coolant while the engine is idling?

Go to Step 15

Go to Step 11

11

Visually inspect the hoses, pipes, and hose clamps at the following locations:

    • The auxiliary heater
    • The coolant bypass
    • The coolant reservoir
    • The heater
    • The radiator

Are any of the hoses, clamps, or pipes leaking?

Go to Step 21

Go to Step 12

12

Visually inspect the following components:

    • The block heater
    • The coolant pressure cap
    • The coolant reservoir
    • The core plugs
    • The cylinder head gaskets
    • The engine block
    • The intake manifold
    • The radiator
    • The thermostat
    • The water pump

Are any of the listed components leaking?

Go to Step 21

Go to Step 13

13
  1. Pressure test the cooling system. Refer to Cooling System Leak Testing .
  2. Visually inspect the components listed in steps 11 and 12 again.

Are any leaks present?

Go to Step 21

Go to Step 14

14

Pressure test the coolant pressure cap. Refer to Pressure Cap Testing .

Does the coolant pressure cap hold pressure?

Go to Step 16

Go to Step 22

15

Pressure test the coolant pressure cap. Refer to Pressure Cap Testing .

Does the coolant pressure cap hold pressure?

Go to Step 33

Go to Step 22

16

Inspect for the following conditions:

    • A coolant smell inside of the vehicle
    • Coolant in the HVAC module drain tube
    • Coolant on the vehicles floor covering under the HVAC module

Is coolant present?

Go to Step 23

Go to Step 17

17

If equipped with auxiliary heating, inspect for the following:

    • A coolant smell inside of the vehicle
    • Coolant in the auxiliary HVAC module drain tube
    • Coolant on the floor covering near the auxiliary HVAC module

Is coolant present?

Go to Step 24

Go to Step 18

18

Inspect the underside of the oil fill cap for a gray/white milky substance.

Is there a milky substance under the oil fill cap?

Go to Step 19

Go to Step 20

19

Inspect the engine oil fluid level indicator for a gray/white milky substance.

Is there a milky substance on the engine fluid level indicator?

Go to Step 24

Go to Step 20

20

Inspect the automatic transmission oil fluid level indicator, if equipped, for a gray/white milky substance.

Is there a milky substance on the automatic transmission fluid level indicator?

Go to Step 26

Go to Step 34

21

Repair or replace the leaking component. Refer to the appropriate repair.

Is the repair complete?

Go to Step 34

--

22

Replace the coolant pressure cap.

Is the repair complete?

Go to Step 34

--

23

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 34

--

24
  1. Remove the engine oil cooler lines from the radiator, if equipped.
  2. Pressure test the cooling system. Refer to Cooling System Leak Testing .
  3. Inspect the engine oil cooler for coolant.

Is coolant present in the engine oil cooler?

Go to Step 25

Go to Step 28

25
  1. Replace the radiator. Refer to Radiator Replacement .
  2. Service the engine oil and filter. Refer to Engine Oil and Oil Filter Replacement for the 4.2L engine or Engine Oil and Oil Filter Replacement for the 5.3L engine.

Is the repair complete?

Go to Step 34

--

26
  1. Remove the transmission oil cooler lines from the radiator.
  2. Pressure test the cooling system. Refer to Cooling System Leak Testing .
  3. Inspect the transmission oil cooler for coolant.

Is coolant present in the transmission oil cooler?

Go to Step 27

Go to Step 28

27
  1. Replace the radiator. Refer to Radiator Replacement .
  2. Service the automatic transmission. Refer to Automatic Transmission Fluid and Filter Replacement .

Is the repair complete?

Go to Step 34

--

28

Install the cooler lines to the radiator.

Is the repair complete?

Go to Step 34

--

29

Repair the engine no crank condition. Refer to Engine Will Not Crank - Crankshaft Will Not Rotate for the 4.2L engine or Engine Will Not Crank - Crankshaft Will Not Rotate for the 5.3L engine.

Is the repair complete?

Go to Step 34

--

30

Repair the engine overheating condition. Refer to Engine Overheating .

Is the repair complete?

Go to Step 34

--

31

Repair the engine internal coolant leak. Refer to Coolant in Combustion Chamber for the 4.2L engine or Coolant in Engine Oil for the 5.3L engine.

Is the repair complete?

Go to Step 34

--

32

Repair the engine knock. Refer to Lower Engine Noise, Regardless of Engine Speed for the 4.2L engine or Lower Engine Noise, Regardless of Engine Speed for the 5.3L engine.

Is the repair complete?

Go to Step 34

--

33

Repair the combustion pressure in the cooling system problem. Refer to Cylinder Leakage Test for the 4.2L engine or Cylinder Leakage Test for the 5.3L engine.

Is the repair complete?

Go to Step 34

--

34

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2