故障现象一辆2009年产奇瑞A5轿车(搭载2.0 L SQR484发动机),散热风扇可以高速运转,但无法低速运转。故障诊断试车发现,随着发动机冷却液温度的升高,散热风扇不会低速运转,而当冷却液温度达到100℃以上时,散热风扇开始高速运转。用故障检测仪检查,读得了故障代码P0480,含义为散热风扇继电器控制电路故障(低速);查看发动机数据流,冷却液温度正常。由该车的散热风扇控制电路(图1)可知,散热风扇控制 Trouble A 2009 Chery A5 sedan (equipped with 2.0 L SQR484 engine), cooling fan can run at high speed, but not at low speed. Diagnostic test found that, as the engine coolant temperature increases, the cooling fan does not run at low speed, and when the coolant temperature reaches 100 ℃ above, the cooling fan began to run at high speed. Check with the fault detector, read the fault code P0480, meaning the cooling fan relay control circuit failure (low speed); view the engine data stream, the coolant temperature is normal. From the car’s cooling fan control circuit (Figure 1) shows, cooling fan control