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Dan
Dan, Auto Technician
Category: Chevy
Satisfied Customers: 3490
Experience:  GM Mark of Excellence/ Service Guild Participant with 13 years experience, ASE Master Certified
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On my 03 Impala, 3.4L, the cooling fans have stopped working.

Customer Question

On my '03 Impala, 3.4L, the cooling fans have stopped working. The cooling fan sensor is good. Mechanic suggested the PCM....
Submitted: 5 years ago.
Category: Chevy
Expert:  Dan replied 5 years ago.
Cooling Fan Inoperative

Step

Action

Yes

No

Schematic Reference: Engine Cooling Schematics

Connector End View Reference: Cooling System Connector End Views

DEFINITION: One or both engine cooling fan motors do not operate properly in high or low speed modes.

1

Did you perform the Engine Cooling Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Engine Cooling

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the Fans Low Speed ON and OFF.

Do the low speed engine cooling fans turn ON and OFF with each command?

Go to Step 3

Go to Step 4

3

Important:: A 3 second delay occurs before the PCM changes the cooling fan speed.

With a scan tool, command the Fans High Speed ON and OFF.

Do the high speed engine cooling fans turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 12

4

    Important: Do NOT remove the 20-A fused jumper wire connected during this step. Use a second 20-A fused jumper wire while performing the following steps.

  1. Remove the FAN CONT #1 relay.
  2. Connect a 20-A fused jumper between the battery positive switch side voltage circuit and the cooling fan motor supply voltage circuit of the FAN CONT #1 relay.

Do both cooling fans operate in low speed?

Go to Step 22

Go to Step 5

5

  1. Disconnect the FAN CONT #2 relay
  2. Connect the second 20-A fused jumper between the cooling fan low reference circuit and the cooling fan motor supply voltage circuit of the FAN CONT #2 relay.

Do both cooling fans operate in low speed?

Go to Step 23

Go to Step 6

6

Connect the second 20-ampere fused jumper between the battery positive voltage circuit and the cooling fan motor supply voltage circuit of the FAN CONT #2 relay.

Does the right cooling fan operate in high speed?

Go to Step 9

Go to Step 7

7

  1. Install the FAN CONT #2 relay.
  2. Disconnect the right cooling fan electrical connector.
  3. Connect the second 20-ampere fused jumper wire from the cooling fan motor supply voltage circuit to the ground circuit of the right cooling fan electrical connector.

Does the left cooling fan operate in high speed?

Go to Step 25

Go to Step 8

8

Connect the second 20-ampere fused jumper wire from the cooling fan motor supply voltage circuit of the right cooling fan electrical connector to a good ground.

Does the left cooling fan operate in high speed?

Go to Step 29

Go to Step 30

9

  1. Install the FAN CONT #2 relay.
  2. Disconnect the left cooling fan electrical connector.
  3. Connect the second 20-ampere fused jumper wire from the cooling fan motor supply voltage circuit to the cooling fan low reference circuit of the left cooling fan electrical connector.

Does the right cooling fan operate in high speed?

Go to Step 26

Go to Step 10

10

Connect the second 20-ampere fused jumper wire from the coil side battery positive voltage circuit to the cooling fan low reference circuit of the of the left cooling fan electrical connector.

Does the right cooling fan operate in high speed?

Go to Step 11

Go to Step 31

11

Probe the battery positive voltage circuit on the switch side of the FAN CONT #1 relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 27

Go to Step 32

12

Is the right cooling fan operating properly in high speed?

Go to Step 19

Go to Step 13

13

  1. Turn off the ignition.
  2. Disconnect the FAN CONT #3 relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the high speed cooling fan relay control circuit and the battery positive voltage circuit on the coil side of the FAN CONT #3 relay.
  5. With a scan tool command the High Speed Fans ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 15

Go to Step 14

14

Probe the battery positive voltage circuit on the coil side of the FAN CONT #3 relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 34

Go to Step 33

15

Install a 20-amp fused jumper between the battery positive voltage circuit on the switch side of the FAN CONT #3 relay and the cooling fan motor supply voltage circuit.

Does the right cooling fan operate in high speed?

Go to Step 24

Go to Step 16

16

Probe the battery positive voltage circuit on the switch side of the FAN CONT #3 relay with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 17

Go to Step 33

17

  1. With the 20 amp fused jumper still installed.
  2. Disconnect the right cooling fan electrical connector.
  3. Connect a test lamp from the cooling fan motor supply voltage circuit to the ground circuit of the right cooling fan electrical connector.

Does the test lamp illuminate?

Go to Step 25

Go to Step 18

18

Probe the cooling fan motor supply voltage circuit of the right cooling fan electrical connector with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 29

Go to Step 30

19

  1. Turn OFF the ignition.
  2. Disconnect the FAN CONT #2 relay
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 20-A fused jumper between the cooling fan low reference circuit and the ground circuit of the FAN CONT #2 relay.
  5. With a scan tool command the Fans High Speed ON and OFF.

Does the left cooling fan operate in high speed?

Go to Step 20

Go to Step 28

20

  1. Connect a test lamp between the high speed cooling fan relay control circuit of the FAN CONT #2 relay and the battery positive voltage circuit of the FAN CONT #2 relay.
  2. With a scan tool command the Fans High Speed ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 23

Go to Step 21

21

Probe the battery positive voltage circuit of the FAN CONT #2 relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 34

Go to Step 33

22

Inspect for poor connections at the FAN CONT #1 relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 40

Go to Step 35

23

Inspect for poor connections at the FAN CONT #2 relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 40

Go to Step 36

24

Inspect for poor connections at the FAN CONT #3 relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 40

Go to Step 37

25

Inspect for poor connections at the harness connector of the right cooling fan. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 40

Go to Step 38

26

Inspect for poor connections at the harness connector of the left cooling fan. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 40

Go to Step 39

27

Repair the left cooling fan motor supply voltage circuit for an open. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

Go to Step 40

--

28

Repair the left cooling fan ground circuit for an open. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

Go to Step 40

--

29

Repair the right cooling fan ground circuit for an open. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

Go to Step 40

--

30

Repair the right cooling fan motor supply voltage circuit for an open. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

Go to Step 40

--

31

Repair the left cooling fan low reference circuit for a short to ground or an open. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

Go to Step 40

--

32

Repair the FAN CONT #1 relay battery positive voltage circuit for an open.

Is the repair complete?

Go to Step 40

--

33

Repair the battery positive voltage circuit for the FAN CONT #2 and #3 relay for an open.

Is the repair complete?

Go to Step 40

--

34

Repair the high speed cooling fan relay control circuit for an open.

Is the repair complete?

Go to Step 40

--

35

Replace the FAN CONT #1 relay.

Is the repair complete?

Go to Step 40

--

36

Replace the FAN CONT #2 relay.

Is the repair complete?

Go to Step 40

--

37

Replace the FAN CONT #3 relay.

Is the repair complete?

Go to Step 40

--

38

Replace the right cooling fan. Refer to Cooling Fan and Shroud Replacement .

Is the repair complete?

Go to Step 40

--

39

Replace the left cooling fan. Refer to Cooling Fan and Shroud Replacement .

Is the repair complete?

Go to Step 40

--

40

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3

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Dan
Dan
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GM Mark of Excellence/ Service Guild Participant with 13 years experience, ASE Master Certified