Diagnostic analysis of how to use automotive oscilloscopes
How to quickly and accurately capture abnormal phenomena and find the cause when diagnosing vehicle faults is the key to solving the problem, and the oscilloscope is an important helper to help maintenance personnel solve this problem. Here is a brief analysis based on the application of oscilloscopes in maintenance diagnosis.
1. The role of digital oscilloscope in automobile maintenance
Some signals of automotive electronic equipment change at a very fast rate, with a change period of one thousandth of a second. Usually the scanning speed of the test instrument should be 5 to 10 times that of the signal being measured. Many fault signals are intermittent and come and go, which requires the testing speed of the instrument to be higher than the speed of the fault signal. Digital oscilloscopes can meet this speed requirement. They can not only capture circuit signals quickly, but also display these waveforms at a slower speed so that maintenance personnel can observe and analyze them at the same time. It can also record signal waveforms in a stored manner, and can go back and observe fast signals that have occurred, which provides great convenience for fault analysis. Whether it is a high-speed signal (such as a fuel injector signal) or a low-speed signal (such as a change in throttle position and oxygen sensor signal), you can find clues from the waveform by observing it with an oscilloscope. An oscilloscope is like a ruler that can measure the working conditions of a computer system. Through an oscilloscope, you can observe how a car's electronic system works.
2. Application of oscilloscope in automobile fault cases
When a car's electronic equipment or wiring fails, maintenance personnel are required to collect all relevant data. An oscilloscope can display the trajectory of electrons in a circuit by displaying the change in voltage over time as a curve. The magnitude of the voltage shown depends on the current and resistance in the circuit. Based on the voltage changes over time on the oscilloscope, you can determine what is wrong with the circuit. To maximize the effectiveness of an oscilloscope, you need to compare the collected waveforms.
Here are a few examples to illustrate how the oscilloscope can help us find the cause of the fault.
Diagnosis of intermittent flameout of Dongfeng Honda Civic
A 2006 Honda Civic 1.8 VTi sedan suffered from intermittent stalling. Connect the oscilloscope to several lines on the engine control unit. In Figure 2, the red line (channel 2) is the camshaft position sensor signal, the green line (channel 3) is the crankshaft position sensor signal, the blue line (channel 4), the white line (channel 5), the purple line (channel 6) and the orange line The yellow lines (channel 7) are the control signals of the four injectors respectively. This set of waveforms was recorded by the oscilloscope when the engine was about to shut down. Please note that the injection sequence of the injectors has been messed up at this time. The purple and orange lines show that the injector control signals inject fuel at the same time. In addition, the injector represented by the orange line has been opened twice in the same period of time compared to other injectors. One important thing is that there is no problem with the camshaft position signal represented by the red line and the crankshaft position signal represented by the green line at this time. Now that we have this information, let's analyze it to find clues for the next step of troubleshooting.
