Electric Cooling Fan Diagnosis. Chevrolet Chevy P32 RV/Van Chassis 1999

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Chevy P32 RV/Van Chassis 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Electric Cooling Fan Diagnosis

Circuit Description

The auxilary cooling fan is controlled by the VCM based on various inputs. Battery voltage is supplied to the auxilary cooling fan relay. Ignition voltage is supplied to the auxilary 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 gage indicated overheating. The gage accuracy can also be checked by comparing the Engine Coolant Temperature (ECT) sensor reading using a scan tool and comparing its reading with the gage reading. If the engine is actually overheating and the gage indicated overheating, but the cooling fan is not coming ON, the Engine Coolant Temperature (ECT) sensor has probably shifted out of calibration and should be replaced.

If the engine is overheating and the cooling fan is ON, the cooling system should be checked, refer to Section 6B.

The VCM will command the auxiliary cooling fan on at 107°C (225°F) and OFF at 103°C (218°F).

Test Description

Number(s) 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	Refer to 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?	--	Refer to 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	Refer to 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 . 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 . 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 . 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 Crankshaft 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