Electric Cooling Fan Diagnosis. GMC Truck GMC Suburban

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC Suburban - 4WD 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Electric Cooling Fan Diagnosis

Engine Controls Components
A/C Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description:

The auxiliary cooling fan is controlled by the VCM based on various inputs. Battery voltage is supplied to the auxiliary cooling fan relay. Ignition voltage is supplied to the auxiliary fan relay (coil side). The VCM controls the cooling fan relay by providing a ground path.

Diagnostic Aids

If the driver complaint is an overheating problem, it must be determined if the complaint was due to an actual boil over, or the warning indicator light, or engine coolant temperature gauge indicated overheating. The gauge accuracy can also be checked by the Engine Coolant Temperature (ECT) sensor reading using a scan tool and comparing its reading with the gauge reading.

If the engine is overheating and the cooling fan is ON, the cooling system should be checked, refer to Engine Overheating in Engine Cooling.

The VCM will command the auxiliary cooling fan on at 108°C (226°F) and OFF at 102°C (215°F).

Test Description

Numbers below refer to step numbers on the diagnostic table.

This test checks the control circuit for a short to ground.

Step	Action	Value(s)	Yes	No
1	Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Important: The engine coolant temperature must be below the specified temperature before continuing with this test. Turn ON the ignition leaving the engine OFF. Is the auxiliary fan OFF?	215° F(102° C)	Go to Step 3	Go to Step 4
3	Command the auxiliary fan motor ON and then OFF with the scan tool. Does the auxiliary fan turn ON and OFF with each command?	--	Go to Diagnostic Aids	Go to Step 5
4	Disconnect the auxiliary cooling fan relay. Is the auxiliary fan OFF?	--	Go to Step 6	Go to Cooling Fan Always On - Auxiliary in Engine Cooling
5	Turn OFF the ignition. Disconnect the auxiliary fan relay. Turn ON the ignition leaving the engine OFF. Probe the auxiliary fan control terminal at the relay connector with a test lamp to B+. Command the auxiliary fan ON using the scan tool. Is the test lamp ON?	--	Go to Cooling Fan Inoperative - Auxiliary in Engine Cooling	Go to Step 8
6	Probe the auxiliary fan control circuit at the fan relay connector with a test lamp connected to B+. Is the test lamp ON?	--	Go to Step 7	Go to Cooling Fan Always On - Auxiliary in Engine Cooling
7	Turn OFF the ignition. Disconnect the VCM C4 connector. Check for a short to ground in the auxiliary fan control circuit between the auxiliary cooling fan relay terminal and the VCM. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find a problem?	--	Go to Step 11	Go to Step 10
8	Check for an open in the auxiliary cooling fan relay control circuit. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find a problem?	--	Go to Step 11	Go to Step 9
9	Check for a poor connection at the VCM. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find a problem?	--	Go to Step 11	Go to Step 10
10	Replace the VCM. Program the VCM. Refer to VCM Replacement/Programming . Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn . Is the action complete?	--	Go to Step 11	--
11	Turn ON the ignition leaving the engine OFF. Command the auxiliary cooling fan motor ON and then OFF with the scan tool. Does the auxiliary cooling fan turn ON and OFF with each command?	--	System OK	Go to Step 2