Symptom: Jetta GIX car 40,000 km idling or traffic jams when the water temperature table rose to 100 degrees.
    Fault check: connect the 5051 fault diagnostic device, enter the engine control unit. Query the fault, trouble-free memory, and then enter the 08 data read 001 area to view the water temperature, from the meter water temperature to 90 degrees when the thermostat open normally, the computer water temperature has been 98 degrees to open the "normal opening time of 96 ~ 99 degrees" Idle conditions, when the water temperature rose to 103.5 degrees, the electronic fan start. 97.5 degrees when the electronic fan off, the temperature of the electronic fan stop a little early, normal for 94.5 degrees before closing, can the car 97.5 degree electronic fan why would it be early when the electronic fan off when the meter temperature rise to 100 degrees or 95 degrees , Until the electronic fan starts to return to normal. This phenomenon is rare, according to the meter water temperature and computer water temperature contrast, there are their many years of experience, can lead to electronic fan closed only the thermostat, so the thermostat to replace, after the test, the water temperature normal , On the road test when the water temperature is normal, troubleshooting.
    Fault analysis: the thermostat by the internal paraffin thermal expansion and contraction principle to control the size of the tank and the engine cycle, electronic fan from the tank on the double temperature switch to control. Water temperature sensor installed in the engine cylinder head on the water pipe, the detection of the engine water temperature. The car failure for the thermostat closed too early lead to a slight high water temperature. The thermostat is closed at 98 degrees, the engine is in a small cycle state, the electronic fan to the water tank inside the water temperature dropped to 94.5 degrees, double temperature switch power, but then the engine is still working temperature rising naturally, the above water temperature malfunction.