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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Cooling 🢒 Cooling Fan Always On - Auxiliary

Cooling Fan Always On - Auxiliary P32/42-Runs With Ignition Off

Step

Action

Value(s)

Yes

No

1

Disconnect the fan control relay. Refer to Cooling System Components .

Does the auxiliary engine coolant fan motor continue to operate?

--

Go to Step 2

Go to Step 3

2

Locate and repair the short to B + in CKT 702 (RED) between the fan control relay and the auxiliary engine coolant fan motor.

Is the repair complete?

--

System OK

--

3

Replace the fan control relay.

Is the repair complete?

--

System OK

--

Cooling Fan Always On - Auxiliary P32 Gas-Runs With Ignition ON

Step

Action

Value(s)

Yes

No

1
  1. Turn the ignition switch to the RUN position.
  2. Disconnect the fan control relay. Refer to Cooling System Components .

Does the auxiliary engine coolant fan motor continue to operate?

--

Go to Step 2

Go to Step 3

2

Locate and repair the short to B + in CKT 702 (RED) between the auxiliary engine coolant fan motor connector and the fan control relay connector.

Is the repair complete?

--

System OK

--

3
  1. Turn the ignition switch to the OFF position.
  2. Disconnect the vehicle control module (VCM) connector C 4.
  3. Inspect CKT 473 (DK BLU) for a short to ground condition.

Did you find a short to ground?

--

Go to Step 4

Go to Step 5

4

Locate and repair the short to ground in CKT 473 (DK BLU) between the VCM connector C 4 and the fan control relay.

Is the repair complete?

--

System OK

--

5
  1. Disconnect the VCM connector C 3.
  2. Connect a test light from the VCM connector C 3, cavity 14 to B +. Refer to Using Connector Test Adapters in Wiring Systems.

Does the test light illuminate?

--

Go to Step 6

Go to Step 9

6
  1. Disconnect the auxiliary engine coolant fan refrigerant pressure switch. Refer to Cooling System Components .
  2. Inspect CKT 604 (DK BLU) for a short to ground condition.

Did you find a short to ground?

--

Go to Step 7

Go to Step 8

7

Locate and repair the short to ground in CKT 604 (DK BLU) between the VCM connector C 3 and the auxiliary engine coolant fan refrigerant pressure switch connector.

Is the repair complete?

--

System OK

--

8

Replace the auxiliary engine coolant fan refrigerant pressure switch.

Is the repair complete?

--

System OK

--

9
  1. Reconnect the VCM connectors C 3 and C 4.
  2. Temporarily replace the fan control relay with a known good part.
  3. Turn the ignition switch to the RUN position.

Does the auxiliary engine coolant fan operate?

--

Go to Step 11

Go to Step 10

10

Replace the fan control relay.

Is the repair complete?

--

System OK

--

11

Refer to Electric Cooling Fan Diagnosis in Engine Controls for VCM-controlled electric cooling fan diagnosis.

Have you completed the VCM diagnostics?

--

System OK

--

Cooling Fan Always On - Auxiliary P32/42 Diesel-Runs w/Ign ON

Step

Action

Value(s)

Yes

No

1
  1. Disconnect the auxiliary engine coolant fan refrigerant pressure switch. For P 32 vehicles, also disconnect the auxiliary engine coolant fan temperature switch. Refer to Cooling System Components .
  2. Turn the ignition switch to the RUN position.
  3. Observe the auxiliary engine coolant fan motor or listen for fan operation.
  4. Turn the igniition switch to the OFF position.

Did the auxiliary engine coolant fan motor operate?

--

Go to Step 2

Go to Step 4

2

Inspect CKT 473 (DK BLU) for a short to ground condition.

Did you find a short to ground?

--

Go to Step 3

Go to Step 8

3

Locate and repair the short to ground in CKT 473 (DK BLU).

Is the repair complete?

--

System OK

--

4

Is the vehicle being repaired a P 32 model?

--

Go to Step 6

Go to Step 5

5
  1. Reconnect the auxiliary engine coolant fan refrigerant pressure switch.
  2. Turn the ignition switch to the RUN position, (engine not running).

Does the auxiliary engine coolant fan motor operate?

--

Go to Step 9

System OK

6
  1. Ensure that the engine coolant is at room temperature.
  2. Reconnect the auxiliary engine coolant fan refrigerant pressure switch.
  3. Turn the ignition switch to the RUN position, (engine not running).

Does the auxiliary engine coolant fan motor operate?

--

Go to Step 9

Go to Step 7

7

Reconnect the auxiliary engine coolant fan temperature switch.

Does the auxiliary engine coolant fan motor operate?

--

Go to Step 10

System OK

8

Replace the fan control relay.

Is the repair complete?

--

System OK

--

9

Replace the auxiliary engine coolant refrigerant pressure switch.

Is the repair complete?

--

System OK

--

10

Replace the auxiliary engine coolant fan temperature switch.

Is the repair complete?

--

System OK

--