GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

Schematic Reference: Engine Cooling Schematics

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

Important: The cooling fan fuses and cooling fan relays 1 and 2 are labeled incorrectly on the underhood sticker. Refer to Electrical Center Identification Views in Wiring Systems for the proper locations.

  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:: Before the PCM changes the speed of the cooling fans, a 3-second delay will occur.

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 11

4

    Important: Following this step, do NOT remove the 20-A fused jumper wire that is connected during this step. While performing the following steps, use a second 20-A fused jumper wire.

  1. Disconnect the cooling fan 1 relay.
  2. Connect a 20-A fused jumper between the battery positive voltage circuit of the cooling fan 1 relay and the cooling fan motor supply voltage circuit of the cooling fan 1 relay.

Do both cooling fans operate in low speed?

Go to Step 13

Go to Step 5

5

  1. Disconnect the cooling fan s/p relay.
  2. Connect the second 20-A fused jumper between the right cooling fan ground circuit of the cooling fan s/p relay and the left cooling fan motor supply voltage circuit of the cooling fan s/p relay.

Do both cooling fans operate in low speed?

Go to Step 14

Go to Step 6

6

Connect a 20-A fused jumper between the battery positive voltage circuit of the cooling fan s/p relay and the cooling fan motor supply voltage circuit of the cooling fan s/p relay.

Does the left cooling fan operate in high speed?

Go to Step 9

Go to Step 7

7

  1. Install the cooling fan s/p relay.
  2. Disconnect the left cooling fan electrical connector.
  3. Connect the second 20-Amp fused jumper wire from the cooling fan motor supply voltage circuit of the left cooling fan electrical connector to the ground circuit of the left cooling fan electrical connector.

Does the right cooling fan operate in high speed?

Go to Step 16

Go to Step 8

8

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

Does the right cooling fan operate in high speed?

Go to Step 20

Go to Step 21

9

  1. Install the cooling fan s/p relay.
  2. Disconnect the right cooling fan electrical connector.
  3. Connect the second 20-Amp fused jumper wire from the cooling fan motor supply voltage circuit of the right cooling fan electrical connector to the cooling fan low reference circuit of the right cooling fan electrical connector.

Does the left cooling fan operate in high speed?

Go to Step 17

Go to Step 10

10

Connect the second 20-Amp fused jumper wire from battery positive voltage to the cooling fan low reference circuit of the of the right cooling fan electrical connector.

Does the left cooling fan operate in high speed?

Go to Step 18

Go to Step 22

11

Is the left cooling fan operating properly in high speed?

Go to Step 12

Go to Step 15

12

  1. Disconnect the cooling fan s/p relay.
  2. Connect the second 20-A fused jumper between the cooling fan low reference circuit of the cooling fan s/p relay and the ground circuit of the cooling fan s/p relay.

Does the right cooling fan operate properly in high speed?

Go to Step 14

Go to Step 19

13

Inspect for poor connections at the cooling fan 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 28

Go to Step 23

14

Inspect for poor connections at the cooling fan s/p 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 28

Go to Step 24

15

Inspect for poor connections at the cooling fan 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 28

Go to Step 25

16

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 28

Go to Step 26

17

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 28

Go to Step 27

18

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

Did you complete the repair?

Go to Step 28

--

19

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

Did you complete the repair?

Go to Step 28

--

20

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

Did you complete the repair?

Go to Step 28

--

21

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

Did you complete the repair?

Go to Step 28

--

22

Repair the cooling fan low reference circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 28

--

23

Replace the cooling fan 1 relay.

Did you complete the repair?

Go to Step 28

--

24

Replace the cooling fan s/p relay.

Did you complete the repair?

Go to Step 28

--

25

Replace the cooling fan 2 relay.

Did you complete the repair?

Go to Step 28

--

26

Replace the left cooling fan. Refer to Engine Coolant Fan Motor Replacement .

Did you complete the repair?

Go to Step 28

--

27

Replace the right cooling fan. Refer to Engine Coolant Fan Motor Replacement .

Did you complete the repair?

Go to Step 28

--

28

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3