Symptom: a 2009 annual production of Dongfeng Honda Civic cars, mileage of 123km. According to the user to reflect the instrument shows the outdoor temperature are not allowed to show the value of -40 ¡æ, and the temperature at 27 ¡æ or so.
Inspection and analysis: First of all, the vehicle to confirm the phenomenon of failure. Open the ignition switch, the instrument on the left side of the odometer shows the outdoor temperature of -40 ¡æ. Ask the user that the new car just bought all the normal, in the modified shop to install a set of fingerprint anti-theft lock after the emergence of the outdoor temperature display is not allowed to the problem.
Because it is the installation of fingerprint anti-theft lock after the failure, we certainly have reason to suspect that is caused by human reasons. As the previous test, will be installed in the front bumper inside the outdoor temperature sensor plug unplugged, the instrument will show -40 ¡æ, so the first step should check the outdoor temperature sensor plug, the result is not loose, then again The installation of anti-theft lock harness part of the inspection, did not find the line was cut off the site. Use Honda dedicated fault diagnosis device HDS into the air conditioning system, read the fault code for the "outside the temperature sensor circuit / short circuit", the fault code does not appear after the removal, but the instrument still shows -40 ¡æ. Further check found that air conditioning to open the automatic (AUTO), the temperature set to the lowest (LO) position, air conditioning system can be cooled, but as long as the temperature increase to some 19 ¡æ, air conditioning central outlet no cool breeze blowing, and Feet blowing warm air, which is the same as the failure of the outdoor temperature sensor open circuit.
The outdoor temperature sensor is a thermistor connected to the air conditioning system control unit. The control unit receives the outdoor temperature signal and passes it through the B-CAN (body communication network) to the instrument module and displays it on the instrument. Remove the outdoor temperature sensor, measuring the resistance value of 1.74kΩ, according to its resistance with temperature changes in the standard range. Disconnect the outdoor temperature sensor plug, open the ignition switch, measuring the voltage in the plug is 4.95V, the initial decision is also normal, at least not open circuit. Just next to a car with the same accident, so the accident car outdoor temperature sensor removed to measure the resistance of 1.67kΩ, and the fault car is not the same, it should not be a problem, but still try to try to mind the plug In the fault car, the results show that the outdoor temperature of 26 ¡æ, is it really the problem of outdoor temperature sensor? Start the car, open the air conditioning AUTO block, air conditioning work is also normal, so a new outdoor temperature sensor installed in the fault car, the results show that the instrument is -40 ¡æ. This is strange, the new outdoor sensor can not be a problem ah! In addition to the accident car outdoor temperature sensor installed, the instrument still shows -40 ¡æ, obviously just replace the test to exclude the fault, how suddenly and bad it? Is it the installation of fingerprint anti-theft lock accidentally broke the air conditioning system control unit? The harness between the 19th and 25th feet of the measuring and control unit and the outdoor temperature sensor plug proves that there is no problem with the wiring harness, and the air conditioning control unit is replaced.
This is strange, the outdoor temperature sensor, air conditioning system control unit and the wiring harness between them are no problem, but why the outdoor temperature or display is not allowed? Try to disconnect the battery negative wiring and then re-installed, the problem is still not resolved, a time do not know where to start from the. Calm down to think about it, and then carefully read the maintenance manual, and found the problem, the maintenance manual on the outdoor temperature sensor logic has the following description.
The outdoor temperature sensor will be initialized when the ignition switch is turned on: If the engine coolant temperature is 60 ° C or higher when the ignition switch is turned ON, the ignition switch will be displayed regardless of the current temperature measurement of the outdoor temperature sensor If the engine coolant temperature is 59 ° C or less when the ignition switch is turned ON, the current temperature of the outdoor temperature sensor is displayed. "See the maintenance manual. Of the instructions, maintenance staff suddenly see the light, the original outdoor temperature sensor display value is also related to the engine water temperature.
Troubleshooting: replace the new outdoor temperature sensor, and so the engine cool down, turn on the ignition switch, the instrument immediately shows the current outdoor temperature of 26 ¡æ, to determine the troubleshooting.
Review Summary: Maintenance personnel in the use of the accident car outside the temperature sensor to replace the fault car outdoor temperature sensor, there is a time to show the current temperature but can not be displayed for a while, this is because the maintenance process with a car , The coolant temperature changes. In this also need to explain "outdoor temperature display in the vehicle during the process of updating." If the current temperature measured by the outdoor temperature sensor is higher than the displayed temperature, the vehicle will accelerate to 30km / h or more and continue for more than 1.5min. The displayed value will increase by 1C per minute and the temperature will continue to rise until the current outdoor temperature. If the vehicle speed is less than 30km / h, the outdoor temperature display will not rise until the vehicle is accelerated to 30km / h or more and lasts for more than 1.5min. If the outdoor temperature is below the displayed temperature, the displayed value is lowered by 1 ° C every 2s until the current outdoor temperature is displayed, which is independent of the vehicle speed.
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