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.
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Engine coolant temperature must be below 100°C (212°F) to perform this test.
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This check can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm the coil may open (amps drop to 0), or short (goes above 0.75 Amp).
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Listen for an audible click when the relay operates. Be sure that both the ON and OFF states are commanded. Repeat the commands as necessary.
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If no trouble is found in the control circuit or the connection at the VCM, the VCM may be faulty, however, this is an extremely unlikely failure.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Install scan tool. Are any DTCs set? | -- | Go to applicable table. | |
Is the cooling fan Off? | 100°C (212°F | |||
4 | Using the scan tool, command the cooling fan relay On and then Off Does the cooling fan turn On and Off with each command? | -- | System OK Refer to Diagnostic Aids | |
5 | Disconnect the cooling fan relay. Does the fan stop? | -- | ||
6 |
Is the test light ON at both circuits? | -- | ||
7 |
Does the test light turn ON and OFF with each command | -- | ||
Is the current draw less than the specified value? | 2 Minutes 0.75 amp | |||
9 |
Is the test light ON? | -- | ||
10 |
Is the resistance at the specified value? | ∞ | ||
11 | Connect a fused jumper wire between the battery feed circuit and circuit leading to the fan motor Does the fan operate? | -- | ||
Does the relay operate? | -- | |||
13 | Check the connections at the fan relay. If faulty connection is found, repair as necessary. Refer to Engine Electrical. Was a problem found? | -- | System OK | |
14 | Check the connections at the VCM. If faulty connection is found, repair as necessary. Refer to Engine Electrical. Was a problem found? | -- | System OK | |
15 | Check the connections at the fan motor harness connector. If faulty connection is found, repair as necessary. Refer to Engine Electrical. Was a problem found? | -- | System OK | |
16 | Repair a short to voltage in the power feed circuit between the fan relay and the fan motor. Is action complete? | -- | System OK | -- |
17 | Check for an open in the power feed circuit between the fan relay and the fan motor. Refer to Engine Electrical. Was a problem found? | -- | System OK | |
18 | Check for an open in the fan motor ground circuit. Refer to Engine Electrical. Was a problem found and repaired? | -- | System OK | |
19 | Repair an open in the battery feed circuit that did not light the test light. Refer to Engine Electrical. Is the action complete? | -- | System OK | -- |
20 | Repair short to ground in the relay control circuit. Was a problem found and repaired? | -- | System OK | |
21 | Check for an open in the fan relay control circuit and repair as necessary. Refer to Engine Electrical. Was a problem found and repaired? | -- | System OK | |
22 | Replace the auxiliary fan relay. Is the fan OFF? | -- | System OK | |
23 | Replace the auxiliary fan motor. Is the action complete? | -- | System OK | -- |
Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | System OK | -- |
