Functional Check - Cooling Fan

Diagnostic Chart - Part 1 of 2:

Diagnostic Chart - Part 2 of 2:

Engine Cooling Fan Control Circuit:

Circuit Description

The cooling fans are controlled by the PCM based on various inputs. Ignition voltage is supplied to all three cooling fan relay coils. The PCM controls cooling fan relay # 1 by providing the ground path. The PCM controls cooling fan relays # 2 and # 3 together by providing a ground path. The left and right cooling fans are connected in series. This will enable both fans on low speed when the fan # 1 relay is energized. When all three fan relays are energized, both fans will operate at high speed. The high speed is possible because the fan relays are wired in a parallel circuit. When the PCM detects that certain DTCs are set, the PCM will enable the cooling fans.

The PCM will enable the engine cooling fans when certain Diagnostic Trouble Codes are set.

Diagnostic Aids

If the owner complained of 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 ECT sensor has probably shifted out of calibration and should be replaced.

If the engine is overheating and the cooling fans are ON, the cooling system should be checked, refer to Cooling System / System Diagnosis. Cooling System

The PCM will command low speed fans ON at 104°C (219°F) and OFF at 95°C (207°F) and, high speed fans ON at 109°C (228°F), and OFF at 103°C (214°F).

Test Description

Number(s) below refer to number(s) on the diagnostic table.

2. The PCM will enable the engine cooling fans when certain Diagnostic Trouble Codes are set. Go to applicable DTC Table first before proceeding with this table.

3. Allow engine coolant temperature to cool below 100°C (212°F) before proceeding with diagnosis.