TOYOTA Alex car, equipped with TOYOTA 2NZ-FE electronic control engine, before the vehicle comprehensive fault diagnosis of the training course, start the vehicle, the engine has the characteristics of starting operation, then self extinguishing. The fault is then checked and diagnosed by the students. Preliminary examination: after receiving the task, first of all the conventional diagnostic methods are used to check the voltage of the battery is 12.46V, normal, the line and other connection parts have not been found abnormal, the engine oil level is normal, the intake pipeline and the seal, the oil inlet pipeline inspection also have no abnormal, and start the vehicle failure phenomenon. Still. Therefore, the ISCV (idle control valve) has a fault, so the use of a multimeter is used to test the engine idle control valve, and the result of resistance and control signal is normal. In addition, it is doubted that the throttle position sensor circuit has fault, and the signal needle of the throttle circuit connector is used to detect the voltage with a pin, and the result signal is normal. Malfunction analysis: self extinguishing from the start and running characteristics of the engine. According to past customary analysis, the circuit fault should be directly judged. But for the 2NZ-FE electronic control system, the main reasons that cause the engine to be unable to start, should consider the following aspects: the most common causes of circuit breakdowns, such as the existence of circuit breakers, short circuits or line splice or other factors; the failure of the power supply of the battery power or the safety box; the electric control of the engine. Failure inside the unit; throttle body or idle control valve malfunction; intake pressure sensor, engine speed sensor failure; related mechanical components caused malfunction. Before doing routine checks, it is also necessary to use a diagnostic instrument to diagnose faults. Diagnostic test: the TOYOTA special computer decoder OBD-II is connected to the DLC3 diagnosis port. The decoder is opened, the model is selected and the fault code is read. The fault code is 4 cylinder P1315, and the fault is described as the ignition line 4#. Next, consult the circuit diagram in the maintenance manual, as shown in Figure 1. During the examination, it was found that the ignition system of the engine was ignited in a static sequence, as shown in Figure 1, combined with the use of a multimeter and inserting the pin in the 1 pin of the 4 cylinder igniter, checking the power + B voltage 12.01V, normal, checking the number of pin (GND) and the resistance of the iron lap to 1.3912, normal, checking the point of the 3 pin. When the IGT is 55.9mV, normal, check the ignition timing feedback signal (IGF) of pin 2 to 0V. In contrast to the 4 cylinder, check the ignition timing feedback signal (IGF) of the same vehicle igniter 2 pin for 4.79V. Troubleshooting: according to the above test, the fault is found on the 2 pin of the 4 cylinder igniter, and the ignition timing feedback signal (IGF) is missing. Therefore, using the 2 pin of the 4 cylinder igniter in the wire connection diagram 1 and the 3 pin (IGF) of the engine ECU connector A, the vehicle starts smoothly, and then checks the resistance of the 2 pin of the 4 cylinder igniter and the 3 pin of the engine ECU connector A. The test result is 00, indicating that the circuit is broken and is checked as the ECU connector A of the engine. The No. 3 pin open circuit was broken down after maintenance. Fault summary: this fault is a teaching case. It describes the general method of vehicle fault diagnosis, detection and final elimination. For the TOYOTA series, if the maintenance personnel can accumulate maintenance experience in peacetime, it can be found that the vehicle can start, but then extinguish the fire, indicating that there is no ignition feedback signal in the control system. If the ignition timing signal is missing, the vehicle can not be started. At present, the communication between the control units on the vehicle is becoming more and more complex. In addition to the need to learn new technologies, the ability of the maintenance personnel to analyze the fault and find the fault parts must be improved to meet the needs of the after-sale service and promote the healthy development of the automobile maintenance industry.