Symptom: A Honda Accord 2.3L sedan, engine model F23A3. The car collided with traffic accidents and the engine room was damaged to a great extent. In order to sheet metal painting operations, the engine as a whole was removed to move outside the car. After the completion of the engine can not start.
    Troubleshooting: According to the customer statement, confirm that the car can not jump fire, to this end, replace the distributor (internally equipped with cylinder identification sensor, referred to as CYP sensor) and ignition coil, or can not start. Using the self-diagnosis method of the electronic control system, the output fault codes are 4 and 8, which indicate the crankshaft position sensor and the top dead center sensor and line abnormality. Both sensors are mounted on the back of the crank pulley. To this end, the sensor module of the oscilloscope were done conduction test, the measured results of the resistance value is infinite, thus replacing the top dead sensor and crankshaft position sensor, but the engine is still suspicious or still can not.
    The use of spark plugs for the fire test, without a little spark. The injector does not have a little action sound, while the fuel pump does not run. After clearing the fault code, use the electronic control self-diagnosis system to see if there are fault anomalies. Connect the SCS short connection to the service diagnostic plug (located below the instrument panel on the side of the passenger's side), turn on the ignition switch ON, and the resulting fault diagnosis (DTC) code is 4 and 8, and there seems to be no exception to the output code The
    Back to the basic inspection, which is the basic operation of the maintenance of electronic control engine steps. Check the fuel injection of the ECU power supply and ground conditions, did not find any exception. But no ignition sparks, fuel nozzles do not move, fuel pump does not run, which is indeed the same as the results of the previous inspection. From this point of view, how to judge should be the engine crankshaft position signal is not input to the ECU control unit. However, the top dead center sensor and the crankshaft position sensor have been replaced, and the connection between the ECU and the sensor will not have any problems, then it is suspected that the ECU itself is a problem. As the final decision ECU evidence of the problem may be quite cautious, because the cost of ECU on the million. Therefore, the oscilloscope can only use the oscilloscope to check the top dead center sensor and crankshaft position sensor output signal waveform. So follow the routine, with the oscilloscope to check the voltage scale and time scale. With the starter to drive the engine running, do not see the output signal voltage waveform. At that time, that is not connected to the probe, check the results of the probe was no problem, try again or no signal voltage waveform.
    In this regard, the oscilloscope watcher voltage scale amplification, try again, the oscilloscope on the screen appears on the signal waveform display sensor only produces 0.2V voltage, the top dead center sensor output voltage is low, the crankshaft position sensor output voltage Low, so that the ECU can not read the engine rotation signal and the piston position signal. The sensor is new and the output signal voltage is so low!
    Measure the resistance of the sensor, but in the provisions of the use of the reference value range. Check the sensor installation status, there is no loose phenomenon. And then feel that the air gap is too large a possibility. Access to the relevant maintenance information, and did not introduce the sensor air gap technical parameters. According to the previous maintenance experience, for the crankshaft position sensor usually the air gap should be between 0.2-0.5mm, otherwise it is difficult to cause changes in the magnetic field lines, of course, not to mention the output signal voltage. Can change the crankshaft position sensor and the top dead center sensor, the most basic operation is to remove the crank pulley, but for the installation of the sensor, but the bolt can be tightened. When the engine rotates it produces a magnetic field line change, not the position of the moving sensor to change the structure of the air gap.
    Since the sensor can not move the location of the air gap is not large, can only be considered that the crankshaft pulley position offset. And then it is suspected that the timing belt moved back from the center of the pulley. With a hand hammer gently hit the crankshaft pulley, and expected the same "despair" sound, pulley moved inward, measured with a vernier caliper, full 6mm. The original is the wheel of the fixed bolt is not tight, the engine is loose when the foot has 3 buckle. Re-tighten the crankshaft pulley fixing bolts by standard torque. Then the ignition switch placed in the starting position, the starter a rotation, the engine will immediately car, troubleshooting!