How to use the car fault diagnostic

Source:http://obd2express.over-blog.com/

The storage contents of multiple failures, analyze and discover their common genesis
In most cases, when reading through DTC troubleshooting functions, will bring up a plurality of the fault records, the contents of these failures sometimes not isolated, often by a hidden failures that result from, or have a certain causal relationship . Failure analysis of the content stored by this point, and then combined with other detection methods and maintenance experience, can quickly determine fault, in this case include two maintenance.

Fault 2: an annual output of 2003 Santana 2000 GSi cars, often fail to start, and then everything is normal after starting. Use the scan tool into the engine electronic control system inquiry, we found that two fault codes are sporadic fault "30-terminal voltage signal is too small" and "no throttle body basic setting" and use Clear fault codes Clear fault recording function , and the throttle basic setting, but for some time after the ignition switch is turned off, the failure occurs again.
It seemed that this initial two engine failures will not lead to accidental can not start properly, but think about it, these two failures have a certain causal relationship. Because the engine control unit via terminal 30 to the control unit fault memory and memory settings provide basic voltage, and maintain long-lasting memories. In the case of the ignition switch is turned off, the 30th terminal voltage is too low or zero, will cause failure to store information and basic settings are lost. When the ignition switch is turned on, the engine can not be started when the query of the fault memory, the fault since the fault voltage terminal 30 basic set too low or zero has been lost, but also caused the above-mentioned "no throttle body basic setting" fault . That is the first fault record is the second leading to the causes of the fault record. After checking circuit it is indeed often the positive power supply terminal of the line into the engine control unit in the center of the plug at the electrical box off the. Reconnect the plug when the engine can not be started again, and then query the actual cause of the fault diagnostic failure is the engine can not be started breaking speed sensor G28, finally put a new engine speed sensor (Fig. 3), the fault completely ruled out.






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   Figure 4

Fault 3: a 2002 annual Guangzhou Honda Accord 2.3 L car can not be started accidentally, fault code query with the Honda PGM fault diagnostic (Fig. 4), four injector open or short circuit fault of the positive electrode, check the injector correlation circuit without any exception. According to experience, four injectors generally not a problem at the same time, but by PGM check out the above injector fault must have some reason. After analysis, the fault should be in control of the four injector common power circuit. In other words, the direct cause of the malfunction is not the fault of the fault diagnostic records are isolated, but identified in the cause of the fault in the injector circuit associated range. According to the injector control circuit and maintenance experience, most likely damage the fuel pump relay, which means that the fuel pump relay may be hidden reasons for the failure record. The fuel pump relay is replaced by a new member, the failure no longer occurs.
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