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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1997 🢒 Yukon - 2WD 🢒 Engine 🢒 Engine Cooling 🢒 Cooling Fan Circuit Diagnosis

Cooling Fan Circuit Diagnosis Fan Inoperative

Auxiliary Cooling Fan Does not Operate

Step

Action

Value(s)

Yes

No

1
  1. Disconnect Auxiliary Cooling Fan Relay.
  2. Connect a test lamp between the Auxiliary Cooling Fan Relay connector cavity 30 to ground.

Does the test lamp light?

Go to Step 2

Go to Step 8

2
  1. Move the Ignition Switch to the Run position.
  2. Connect a test lamp between Auxiliary Fan Relay connector cavity 85 to ground.

Does the test lamp light?

Go to Step 3

Go to Step 9

3
  1. Connect a fused jumper between the Auxiliary Cooling Fan Relay connector cavity 30 to cavity 87.

Does the Auxiliary Cooling Fan Motor run?

Go to Step 5

Go to Step 4

4
  1. Connect a self-powered test lamp between the Auxiliary Cooling Fan Motor connector cavity A and ground.

Does the test lamp light?

Go to Step 10

Go to Step 11

5
  1. Move the Ignition Switch to the Off position.
  2. Disconnect all Vehicle Control Module (VCM) connectors.
  3. Connect a self-powered test lamp between VCM connector C4 terminal 6 and Auxiliary Cooling Fan Relay connector cavity 86

Does the test lamp light?

Go to Step 6

Go to Step 12

6
  1. Re-connect Auxiliary Cooling Fan Relay.
  2. Move the Ignition Switch to the Run position.
  3. Connect a fused jumper between VCM connector C4 terminal 6 and ground.

Does the Auxiliary Cooling Fan Motor run?

Go to Step 7

Go to Step 13

7
  1. Leave the Ignition Switch in the Run position.
  2. Push the Recirculation button on the Heater and A/C Control Panel in to the On position.
  3. Connect a test lamp between VCM connector C4 terminal 7 and B+.

Does the test lamp light?

Go to Step 14

Go to Step 15

8

Repair open in the ORN (1540) wire between the Underhood Fuse Relay Center and the Auxiliary Cooling Fan Relay.

9

Repair open in ORN (1250) wire between the Underhood Fuse Relay Center and the Auxiliary Fuse Relay Center.

10

Check for an open in RED (702) wire between the Auxiliary Cooling Fan Relay and the Auxiliary Cooling Fan Motor. If OK, Replace Auxiliary Cooling Fan Motor.

11

Repair open in BLK (250) wire between the Auxiliary Cooling Fan Motor and G112.

12

Repair open in DK BLU (473) wire between the VCM and the Auxiliary Cooling Fan Relay.

13

Replace the Auxiliary Cooling Fan Relay.

14

Refer to Section 6 Engine Controls for further diagnostics.

15

Check for an open in DK GRN (1614) wire between the VCM and the Heater and A/C Control Module. If OK, Replace the Heater and A/C Control Module.

Cooling Fan Circuit Diagnosis Fan Runs at all Times

Auxiliary Cooling Fan is On at all Times

Step

Action

Value(s)

Yes

No

1
  1. Disconnect the Auxiliary Cooling Fan Relay.

Does the Auxiliary Cooling Fan Motor stop?

Go to Step 2

Go to Step 4

2
  1. Ensure that the Ignition Switch is in the Off position.
  2. Disconnect all Vehicle Control Module (VCM) connectors.
  3. Connect a self-powered test lamp between VCM connector C4 terminal 6 and ground.

Does the test lamp light?

Go to Step 5

Go to Step 3

3
  1. Ensure that the Recirculation button in the Heater and A/C Control Module is out or in the Off position.
  2. Connect a self-powered test lamp between VCM connector C4 terminal 7 and ground.

Does the test lamp light?

Go to Step 6

Go to Step 7

4

Repair short to voltage in RED (702) wire between Auxiliary Cooling Fan Relay and Auxiliary Cooling Fan Motor.

5

Repair short to ground in DK BLU (473) wire between Auxiliary Cooling Fan Relay and VCM.

6

Repair short to ground in DK GRN (1614) wire between VCM and Heater and A/C Control Module.

7

Replace Auxiliary Cooling Fan Relay.