In 1992, the Toyota Corona sedan equipped with the 3S-FE engine occasionally has a flameout in the course of driving, but it can be started immediately after the flame. This time no reason to turn off the engine can not start.
    After the car check results are as follows: 1. engine start without high pressure fire; 2. engine fuel injection nozzle can not measure the fuel injection pulse; 3. open the ignition switch, engine failure warning light does not light (normally open the ignition switch, The engine fault light should be lit. After the engine starts the electronic control unit on the electronic control components for 4 ~ 6s self-test to confirm the fault when the fault light is always bright, no fault when the fault light goes out). Taking into account the car ignition and fuel injection are directly controlled by the ECU, it is likely that the ECU lacks the operating voltage and can not work due.
    First check ECUEFI insurance, insurance without burning phenomenon. With a dedicated engine fault detector for testing, detector display no communication links. With a short connection to connect the diagnostic plug TE1 feet and E1 feet, to manually read the fault code, fault light is still not bright. In order to prevent E1 feet off bad, directly to the TE1 feet ground, fault lights did not respond. The owner reflects the fault light before the repair is good. This is more sure that the engine does not fire is caused by the ECU does not work.
    Find all the power lines BATT, + B, + B1 and all ground lines E, E01, E02 of the ECU, as shown in the figure, are found to be normal. We had to remove the ECU shell, its internal components for testing. Measured by the input line of fire, the cable can be sent to the ECU internal, pin no problem, and its internal components are not significantly burned, open welding phenomenon. In order to further determine the quality of the computer, we have to replace the ECU assembly comparison test. The replacement of a normal driving the same model on the ECU after the start of the test, still can not catch the fire. And the car ECU installed on the normal car, the engine can start the fire once, and the engine fault detector can communicate with the ECU, the engine conditions are normal, indicating that the car computer is intact, then the reason out Where?
    To this end, had to press the circuit diagram of the lines carefully "inventory." When the throttle valve operating voltage is detected, suddenly light up. The working voltage is not even 5V, only less than 0.7V voltage. It can be seen from the part of the circuit diagram, the intake pressure sensor, throttle opening sensor and CO concentration regulator variable resistor three share a power cord, the power regulator sent by the ECU, the normal value should be 5V.
    Replacement ECU comparison experiment has been determined ECU is normal, then it should be able to send 5V normal voltage. Must be on the line somewhere there is a short circuit caused by the voltage drop on the line is too large. Unplug the ECU plug, unplug the throttle position sensor plug, measure the throttle position sensor harness side line 4 (working power) to ground resistance, found less than 1Ω, abnormal value. Unplug the intake pressure sensor plug and measure the harness side line 3 (working power) to ground resistance and find that it is also only 1Ω. Check the CO concentration regulator variable resistor, pull out the variable resistor plug, wire harness side line 3 to ground resistance, found with the harness shaking its resistance sometimes infinite, sometimes 0. This shows that there may be a problem with the wiring harness of the CO concentration regulator.
    The inspection revealed that the harness was passed from below the bottom of the fender and was pierced by a small hole in the fender located at the right headlamp and connected to the variable resistor located there. Remove the wing liner to pull out the wire harness and check that the wire has been squeezed out at a distance from the plug, and that the copper wire has been peeled off from the outer insulation. Bandaged wire harness and re-fixed harness, CO concentration regulator variable resistor, start the engine, start the fire, troubleshooting.
    According to the owner to reflect, six months ago the car had an accident, and replaced the bumper, the right side of the fender and the right lights. It is necessary to replace the bumper and the fender when the harness did not notice the harness damage. At the same time the damaged wiring harness did not immediately cause failure, with the future driving vibration and wave, wiring harness fixed point loose. Coupled with the cold and cold deformation of the wiring harness, making the wiring harness directly contact with the fender, resulting in 5V voltage directly with the car body short circuit. When the short-circuit current is too large, the ECU can not work.
    This short circuit on the line is different from our usual common within a short circuit of electrical components. It can be seen from the circuit diagram, the water temperature sensor, intake air temperature sensor, throttle position sensor and other components of the power line and ground line are provided by the computer to form a closed circuit. On the one hand to rely on reliable; the other hand, the electrical components and ECU constitute a circuit can be monitored. Once the electrical components within the short circuit, due to the ECU protection circuit adjustment, it will not make the current consumption is too large. At the same time ECU enabled standby program, you can slowly go home will not stop halfway. But when the external components of the circuit and the car body, the ECU can not control the current, it will cause ECU work disorders, and even ECU bridge circuit imbalance and not work, also led to the engine without the phenomenon of the car.
    A small line of short circuit failure even spent more than 3 days time, and finally found to be the previous maintenance left the "tail". Vehicle maintenance is the maintenance efficiency and maintenance of the organic unity of quality, not only for maintenance efficiency, while ignoring the quality of maintenance. In the maintenance process to pay attention to prevent the tide, not because it is only a small negligence, a small fault on the area, or in the future will lead to a big mistake. The old saying is good, "not because of good and small, not because of evil and small." Thousands of miles of embankment in the nest, the philosophy of which fascinated deep.