GM Service Manual Online
For 1990-2009 cars only
Table 1: Electric Cooling Fan Functional Check
Table 2: Electric Cooling Fan Table #1
Table 3: Electric Cooling Fan Table #2
Table 4: Electric Cooling Fan Table #3

Circuit Description

Power for the fan motors is supplied through the underhood accessory wiring junction block. The cooling fan relays are energized when current flows from the fan control 1 fuse and the fan 2 and 3 control fuse in the underhood accessory junction block through the relay coils to ground through the powertrain control module (PCM). The low speed fans control circuit is grounded for low speed fans operation. The low speed fans control circuit and the high speed fans control circuits are all grounded for high speed fans operation.

During low speed fans operation the PCM supplies a ground path for the cool fan 1 relay. This closes cool fan 1 relay contacts, allowing current to flow from the underhood accessory junction block through the relay contacts to the right cooling fan motor. During low speed operation, the ground path for the right cooling fan motor is through the cool fan 2 relay and the left engine cooling fan motor. The result is a series circuit with both cooling fans running at low speed.

During high speed cooling fan operation the PCM supplies a ground path for the cool fan 1 relay. The PCM also supplies a ground path for cool fan 2 and cool fan 3 relays. This closes all 3 cooling fan relays. During high speed fans operation, both the right and the left engine cooling fans are supplied current from the underhood accessory junction block and each cooling fan has a ground path.

Diagnostic Aids

If the owner complained of an overheating problem, determine if the complaint was due to an actual boil-over, the warning indicator illuminated, or the engine coolant temperature (ECT) gauge indicated overheating. The gauge accuracy can also be checked by comparing the ECT sensor reading using a scan tool and comparing its reading with the gauge reading. If the engine is actually overheating and the gauge indicated overheating, but the cooling fans are not turning on, the ECT sensor may have shifted out of calibration and should be replaced. If the engine is overheating and the cooling fans are on, the cooling system is suspect and should be checked.

Inspect for the following conditions:

    •  A poor connection at the PCM, the cooling fan relays, or the cooling fan motors. Inspect the harness connectors for the following conditions. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems:
       - Backed-out terminals
       - Improper mating
       - Broken locks
       - Improperly formed or damaged terminals
       - Poor terminal-to-wire connections
    • A damaged harness. Inspect the wiring harness for damage. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Test Description

The numbers below refer to numbers on the diagnostic table:

  1. The PCM will enable the engine cooling fans when certain Diagnostic Trouble Codes are set. Go to applicable DTC Table first before proceeding with this table.

  2. Allow engine coolant temperature to cool below 100°C (212°F) before proceeding with diagnosis.

Electric Cooling Fan Functional Check

Step

Action

Values

Yes

No

1

Did you perform the Powertrain OBD System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are any DTCs set?

--

Go to applicable DTCs

Go to Step 3

3

  1. Install a scan tool.
  2. Engine coolant temperature must be below the specified value for all the fan diagnoses.
  3. Turn on the Ignition, with the engine and A/C off.

Are the cooling fans off?

100°C (212°F)

Go to Step 4

Go to Cooling Fan table #1

4

With a scan tool, command Low Speed Fans on.

Are both cooling fans on?

--

Go to Step 5

Go to Cooling Fan table #2

5

Important: :  Allow a 3-5 second delay before determining if the fans have switched from low to high speed.

With a scan tool, command High Speed Fans on.

Do both cooling fans switch to high speed?

--

Go to Step 6

Go to Cooling Fan table #3

6

  1. Exit outputs screen on the scan tool.
  2. Idle the engine leaving the A/C off.

Are the cooling fans on?

--

Go to Step 8

Go to Step 7

7

Turn on the A/C.

Are the cooling fans on?

--

System OK

Go to Step 9

8

Does the scan tool display A/C request as YES?

--

Go to Cooling Insufficient - Air Conditioning (A/C) System in Heating, Ventilation, and Air Conditioning

Go to Step 10

9

Does the scan tool display A/C request as YES?

--

Go to Air Conditioning (A/C) Compressor Control Circuit Diagnosis

Go to Cooling Insufficient - Air Conditioning (A/C) System in Heating, Ventilation, and Air Conditioning

10

Important: :  The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

System OK

--

Electric Cooling Fan Table #1

Step

Action

Values

Yes

No

1

Did you perform the Cooling Fan Functional Check?

--

Go to Step 2

Go to Cooling Fan Functional Check

2

Disconnect Cool Fan 1 Relay.

Are both fans off?

--

Go to Step 8

Go to Step 3

3

Disconnect Cool Fan Relay.

Are both fans off?

--

Go to Step 4

Go to Step 10

4

  1. Disconnect the left fan.
  2. Probe terminal B of the left fan connector using a test lamp that is connected to a known good ground.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 5

5

Probe terminal A of the left fan connector using a test lamp that is connected to a known good ground.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 6

6

Probe the High Speed Fans control circuit (473) at the Cool Fan Relay connector in the

Underhood Accessory Wiring Junction Block Label


Object Number: 643829  Size: MF
using a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 13

7

  1. Turn off the ignition.
  2. Leave the test lamp installed.
  3. Disconnect the PCM.
  4. Turn on the ignition, with the engine off.

Is the test lamp still illuminated?

--

Go to Step 14

Go to Step 16

8

Probe the Low Speed Fans Control circuit (335) at the Cool Fan 1 Relay connector using the test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 13

9

  1. Turn off the ignition.
  2. Leave the test lamp installed.
  3. Disconnect the PCM.
  4. Turn on the ignition, with the engine off.

Is the test lamp still illuminated?

--

Go to Step 14

Go to Step 16

10

Repair the RH fan feed circuit (409) for a short to voltage. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Cooling Fan Functional Check

Go to Step 15

11

Repair the LH fan feed circuit (532) for a short to voltage. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

12

Repair the short to voltage in the Cool Fan Relay feed circuit (504). Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

13

Replace the Cool Fan 1 Relay.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

14

Repair the High Speed Fans Control circuit (473) or the Low Speed Fans Control circuit (335) for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

15

Replace the Cool Fan Relay.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

16

Important::  Program the replacement PCM.

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming .

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

Electric Cooling Fan Table #2

Step

Action

Values

Yes

No

1

Did you perform the Cooling Fan Functional Check?

--

Go to Step 2

Go to Cooling Fan Functional Check

2

Did either fan turn on when Cool Fan 1 Relay was commanded on?

--

Go to Step 3

Go to Step 5

3

  1. Install a scan tool.
  2. With a scan tool, command High Speed Fans on.

Did the other fan turn off?

--

Go to Step 19

Go to Step 4

4

With the Low Speed Fans Commanded ON, Disconnect Cool Fan Relay.

Did the left fan turn off?

--

Go to Step 20

Go to Step 21

5

  1. Disconnect Cool Fan 1 Relay.
  2. Probe Low Speed Fans Control circuit (335) at the Cool Fan 1 Relay Connector using a test lamp that is connected to battery positive voltage.
  3. With a scan tool, command Low Speed Fans on.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 13

6

Probe both feed circuits (342) at the Cool Fan 1 Relay Connector using a test lamp that is connected to ground.

Does test lamp illuminate for both circuits?

--

Go to Step 7

Go to Step 22

7

Important: :  Leave jumper in place for remainder of this table.

Connect a fused jumper wire between the switch feed circuit (342) and the LH fan feed circuit (532) at the Cool Fan 1 Relay Connector.

Do both fans turn on?

--

Go to Step 23

Go to Step 8

8

  1. Disconnect the left fan.
  2. Probe fan harness connector terminal B with a test lamp that is connected to a known good ground.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 24

9

Connect a second fused jumper wire between the left fan harness connector terminals.

Is the right fan on?

--

Go to Step 16

Go to Step 10

10

  1. Reconnect the left fan.
  2. Disconnect Cool Fan Relay.
  3. Probe the switch feed circuit (504) at Cool Fan Relay connector using a test lamp that is connected to a known good ground.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 25

11

Using a second jumper wire, jumper the switch feed circuit (504) and the RH fan feed circuit (409) together at Cool Fan Relay connector.

Do the fans come on?

--

Go to Step 26

Go to Step 12

12

  1. Reconnect Cool Fan Relay.
  2. Disconnect the right fan.
  3. Probe right fan harness connector terminal B with a test lamp that is connected to a known good ground.

Is the left fan on?

--

Go to Step 16

Go to Step 18

13

  1. Keep the test lamp connected.
  2. Turn off the ignition.
  3. Disconnect the PCM.
  4. Probe the Low Speed Fans Control circuit at the PCM connector, with a fused jumper wire that is connected to a known good ground.

Did the test lamp illuminate?

--

Go to Step 20

Go to Step 21

14

Inspect the PCM connections. Repair faulty connections as necessary. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Cooling Fan Functional Check

Go to Step 27

15

Repair the Low Speed Fans Control circuit (335) for an open or shorted to battery positive voltage. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

16

Inspect the fan motor ground circuit for a open or the fan motor connections. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs or Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Cooling Fan Functional Check

Go to Step 17

17

Replace the faulty fan motor. Refer to Engine Cooling Fan Replacement in Engine Cooling.

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

18

Repair the RH fan feed circuit (409) for an open. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

19

Replace the fan which was not operating. Refer to Engine Cooling Fan Replacement in Engine Cooling.

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

20

Replace Cool Fan Relay.

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

21

Repair the Cool Fan Relay feed circuit (504) for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Cooling Fan Functional Check

Go to Step 26

22

Repair the open or the grounded circuit for the circuit that did not light. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

23

Replace Cool Fan 1 Relay.

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

24

Repair the LH fan feed circuit (532) for an open. Refer to Wiring Repairs in Wiring Systems.

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

25

Repair the Cool Fan Relay switch feed circuit (504) for an open. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

26

Replace Cool Fan Relay .

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

27

Important: :  Program the replacement PCM.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

Electric Cooling Fan Table #3

Step

Action

Values

Yes

No

1

Did you perform the Cooling Fan Functional Check?

--

Go to Step 2

Go to Cooling Fan Functional Check

2

  1. With a scan tool, command Low Speed Fans on.
  2. Command High Speed Fans on.

Did both fans operate with no change?

--

Go to Step 8

Go to Step 3

3

Did the left fan stop operating?

--

Go to Step 9

Go to Step 4

4

  1. Disconnect Cool Fan 2 Relay.
  2. Probe the High Speed Fans Control circuit (473) at Cool Fan 2 Relay connector using a test lamp that is connected to battery positive voltage.
  3. Command High Speed Fans on using a scan tool.

Does the test lamp illuminate after several seconds?

--

Go to Step 5

Go to Step 12

5

Probe the coil feed circuit (1442) at Cool Fan 2 Relay connector using a test lamp that is connected to a known good ground.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 13

6

Probe the switch feed circuit (1442) at the Cool Fan 2 Relay connector using a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 14

7

Jumper the switch feed circuit (1442) and the RH fan feed circuit (409) together at the Cool Fan 2 Relay connector.

Is the right fan on?

--

Go to Step 15

Go to Step 16

8

  1. Turn off the ignition.
  2. Disconnect the PCM.
  3. Disconnect Cool Fan 1 Relay.
  4. Jumper the switch feed circuit (342) and the RH fan feed circuit (532) together at the Cool Fan 1 Relay connector.
  5. Turn the ignition on.
  6. Probe the PCM harness connector for the High Speed Fans Control circuit with a fused jumper that is connected to a known good ground.

Do the fans switch from low to high speed?

--

Go to Step 22

Go to Step 17

9

  1. Disconnect Cool Fan Relay.
  2. Probe the High Speed Fans Control Cirucit (473) at the Cool Fan Relay connector using a test lamp that is connected to battery positive voltage.
  3. Command High Speed Fans on using a scan tool.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 18

10

Probe the ground circuit (1050) at the Cool Fan Relay connector using a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 19

11

Probe the coil feed circuit (1442) at the Cool Fan Relay connector using a test lamp that is connected to a known good ground.

Does the test lamp illuminate?

--

Go to Step 20

Go to Step 21

12

Repair the High Speed Fans Control circuit (473) for an open between Cool Fan Relay and the splice. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

13

Repair the open in the Cool Fan 2 Relay coil feed circuit (1442). Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

14

Repair the open in the Cool Fan 2 Relay switch feed circuit (1442). Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

15

Replace Cool Fan 2 Relay.

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--

16

Repair the open in the RH fan feed circuit (409) between Cool Fan 3 Relay and the splice. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

17

Repair the High Speed Fans Control circuit (473) for an open or for a short to battery positive voltage. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

18

Repair the open in the High Speed Fans Control circuit (473) between Cool Fan Relay and the splice. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

19

Repair the open in the ground circuit (1050). Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

20

Replace the Cool Fan relay.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

21

Repair the open in Cool Fan Relay coil feed circuit (1442). Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Cooling Fan Functional Check

--

22

Inspect the PCM connections. Refer to Testing for Intermittent Conditions and Poor Connections , and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Cooling Fan Functional Check

Go to Step 23

23

Important: :  Program the replacement PCM.

Replace the PCM.Refer to Powertrain Control Module Replacement/Programming .

Did you complete the replacement?

--

Go to Cooling Fan Functional Check

--