Fault diagnosis: 1) first, the ignition system is checked when the fault occurs, all of which are normal, then the fuel pressure meter is attached to the fuel line, and a 21W test lamp is parallel in the joint of the oil pump to synchronize the oil supply condition and work condition of the oil pump. 2) twist the key to the ON position, the oil pressure rises to 270kPa, the test lamp lights up, start the engine, the test lamp is not bright, start the engine, work normally. 3) failure occurs when the key is screwed to the ON position after the fire is turned off. The test lamp is not lighted and the oil pressure gauge does not change. The static pressure of the system is generally lower than the working pressure, so the oil pressure should rise when the key is screwed to the ON position after the quenching is put out, so the fault is suspected to be in the main PGM-Fl relay. 4) check the PGM-Fl main relay, connect the light emitting diode between the positive pole of the battery and the A15 foot in the ECM/PCM. After many open keys, the fault appears, the light emitting diode is bright, the test lamp and the oil pressure meter are not changed, and it is determined to be the fault of the main relay of the PGM-F1. 5) after the replacement of the PGM-F1 main relay, the fault is eliminated. Maintenance summary: the engine oil pump is controlled by the PGM-Fl main relay 1 and the PGM-F1 main relay 2. When the key is screwed to the ON position, the PGM-F1 main relay 1 is absorbed and delivered to the computer, the injector and the PGM-Fl main relay 2. After receiving the output signal of the PGM-Fl main relay 1, the computer sends the 2S signal to the foot of the PGM-Fl main relay (oil pump relay) A15 foot, so that the oil pump relay is absorbed in 2S and accumulating pressure for the fuel system. The light emitting diode is connected between the A15 foot and the positive pole of the battery in order to check whether the PGM-Fl main relay and the computer work properly, and whether the oil pump relay is triggered by the trigger signal. When the oil pump relay fails, the residual pressure in the system makes the engine still start, but as the oil pressure decreases, the engine dies out gradually. Due to the unstable operation of the oil pump relay, when the oil supply is insufficient or no oil is supplied, the engine is difficult to start again or fails to start.