水温传感器引发的疑难故障

水温传感器引发的疑难故障 A Shanghai buick car, users reflect the vehicle starting difficulty, every time a starting three or four times the engine to the car, and the vehicle idle instability will occur after starting, hot water temperature is high, after the car exhaust smoke and throttle back easily flame-out phenomenon, at the same time the engine failure indicator sometimes normally on not extinguish. Inspect the car after coming to the factory and find that there is almost no sign of a car when it is not on the accelerator pedal. After stepping on the gas pedal, it is normal to start up, but the engine will not be able to lift the accelerator, and the engine will stall. But if you're stuck on the gas pedal after the car, you're going to slow down after a while On the accelerator pedal, the engine can run, but just step on the gas pedal and the engine is out of the fire. There was a slight improvement in the hot car, but it still happened. In fact, this type of failure occurs in other cars, mostly because of the serious damage caused by the dirty or idle control valves. And fault point lies mainly in air inflow is restricted, because cool car starting, the volume is relatively more, though the computer will control the idle speed control valve, but it requires a process. So a lot of time because of the throttle body dirty or idle speed control valve caused the car appear such serious fault formation, but the fault is rarely causes trouble light normally on not extinguish. After the hot car, the inspection also found that the electronic fans did not turn. But for the sake of safety, I first checked and cleaned the intake system. The results of the inspection are good for all piping connections in the air inlet system, no leakage, no plugging, and the throttle position sensor and idle control valve work well. Only the line of the car was confused, from the appearance of the fire, and the line of the idle control valve and the throttle position sensor was followed. In response to this situation, the author USES the fault diagnosis instrument to check the electric control system of the engine. It was found that the "P0117: water temperature sensor circuit voltage was too low". In addition, the temperature that the diagnostic data stream reflects is not consistent with the actual water temperature. Diagnostic instrument display water temperature is 39 ?, indicating that water temperature sensor circuit happens, because - 39 ? is a computer in the test is less than the water temperature signal after the execution of a default value. Then I check the water temperature sensor, the engine water temperature is about 30 ?, measured the resistance value is about 2400 Ω, belongs to the normal; When the engine temperature is about 90 ?, about 240 Ω measured the resistance value, also is normal, the water temperature sensor itself trouble-free. Then the author examined the sensor wiring harness plug, use multimeter measuring sensor has a 5 V voltage between two terminals, PCM (engine computer) seemed to water temperature sensor power supply voltage is normal. So why do you have a temperature sensor failure code, and a failure to do so? I decided to clear the failure code first. It can be found in the course of the cleaning process that the failure codes cannot be removed, either by using the diagnostic instrument or by taking down the anode. After repeated examination, the author found that even if the engine was not starting, if the ignition switch was turned on and the fault was read directly, the P0117 would exist. This is strange, is the PCM unable to receive the signal from the water temperature sensor, or is the computer broken and the memory in PCM can't be cleared? But the temperature sensor of this car is all from PCM, and it is normal to be measured. Where is the problem? Observed with doubt I remove the PCM, wiring harness and PCM terminal have corrosion, use brush to remove dirt, and careful observation of circuit board and components and no damage, for casual wear. After that, the car was tried again, but the problem was not ruled out. Later, I retook the error code and found that there was a "P0107" fault in addition to the P0117. Did the gas pressure sensor go wrong again? But based on the engine operation and emissions are very normal, not on the inlet pressure device to remove the check too much, just observe the plug contact situation, found that good contact. The error code was cleared and then the fault code, P0107 no longer appeared, but P0117 still existed. This is strange, if PCM's self-diagnosing dysfunction, why is it normal to read and clean P0107? So I pulled out the plug of the injector, and found the error code and the removal of the error code. At this point, the author carefully analyzes the failure of the car, and according to the above examination results, the fault should be on the line. Given that the car's wiring has been burned, there is likely to be a bad connection. I first measured the voltage of the PCM terminals, including the voltage of the power supply and the voltage of the actuators. During the inspection, a simulated fault was also used, and the edges were dithered as far as possible to see if there was a bad connection. The final test results show that the data of the power supply voltage and other sensors are in the normal range, only the terminal voltage of the temperature sensor is abnormal. Normally, the voltage value between the signal source terminals and the ground terminals of the temperature sensor on the ignition switch should be 5 V. And although the actual measured result is 5 V, but the using data at the sensor simulator directly provide different resistance to signal lines, water temperature values are read from the diagnostic instrument is always - 39 ?, electronic fan does not turn, this shows that the water temperature sensor circuit is indeed break phenomenon. The author with multimeter carefully measured the water temperature sensor for this line, found the 5 V power supply without any problem, the output of the computer directly to the sensor, and computer output ground wire is not entirely entering water temperature sensor, the circuit phenomenon. No wonder the simulated water temperature sensor is not allowed to enter the computer, and the fault disappears after connecting a ground line from the computer's output to the water temperature sensor. After five hours of repeated searching, the failure was finally ruled out. But looking back at the whole troubleshooting process, it really took a lot of trouble. But the ground breaking in advance to check the water temperature sensor circuit not found, because the wire close to the body on the edge, grinding broken after disconnection, but bare threads and there are connections between body (of course is virtual, but when measuring the contact). This way, the line is checked on one side of the sensor and there is an iron in the PCM side, so it is not easy to find. Range for each open ignition switch engine running P0117 fault code will always happen, because PCM was obtained in the process of water temperature transducer signal in the circuit. In addition, the failure code is not uncleared, but is read first.