Land Rover found that the water temperature meter of 3 diesel 2.7T car does not work
  • Automotive

A 3 diesel 2.7T sedan was found in a Land Rover produced in December 2007. The malfunction of the car is that the water meter does not work. Test the water temperature sensor, normal (also change); test the water temperature sensor to the engine computer line, normal; test the engine computer to the instrument high speed CAN, the connection normal; instrument iron also normal. Detection with fault diagnosis instrument, no fault code. The data flow shows that the water temperature is normal, the water temperature sensor plug is pulled out, the water temperature indicator is alarm and the water temperature pointer reaches the highest, and the water temperature sensor joint is inserted at once, and the water temperature pointer is reduced to the lowest. Try to replace the two times the instrument temperature of the electronic stepper motor, invalid, find the same vehicle type instrument test, nor can it. Now it is suspected that there is a problem with the engine computer, but there is no basis for it. Please help solve it. The water temperature sensor is a thermistor made of semiconductor material. The resistance value can be predicted and changed with the change of temperature. At 40 C, the resistance value may be 100k ohm, and at 100 C, it may be between 100~200 ohms. Even very small temperature changes can be observed by measuring the resistance changes of thermistors. This characteristic makes thermistor an ideal tool for measuring temperature, and can measure the temperature of engine coolant or air. There are two kinds of thermistors: negative temperature coefficient (NTC) and positive temperature coefficient (PTC). The negative resistance of the thermistor decreases with the increase of temperature, and the resistance of the thermistor with positive temperature coefficient increases with the increase of temperature. Most thermistors, including temperature sensors for automotive computer control systems, are negative temperature coefficient types. The computer sends a 5V adjustment voltage signal to the coolant temperature sensor through a fixed resistance, and a small current flows through the thermistor, then returns to the place. This is a voltage divider circuit (current flows through the first resistor and then flows through second resistors), often used as a temperature sensor circuit. Because the resistance of the thermistor varies with temperature, the voltage drop at the two ends of the sensor changes accordingly. The computer monitors the voltage drop at both ends of the thermistor, and then uses the pre compiled data to convert the voltage drop to the corresponding temperature value. If you understand this, in parallel or in series, change the voltage of the temperature sensor at both ends of the water temperature sensor, then the computer data has no corresponding changes, can be diagnosed as a computer problem. And through your description, the inspection is checked, and all the changes have been changed. Basically, it can be diagnosed as a computer problem.