Vehicle occasionally won’t start, what causes it? How to check?

Vehicle information

A SAIC RWD vehicle with engine model 18K4G has recently been giving feedback of a constant engine fault light, occasional failure to start, and poor acceleration.

maintenance process

1. Diagnostic computer testing found that the ECM module has the following fault code try to clear the fault code after the test drive, P0321 fault still exists.
2. Refer to the diagnostic manual, check the ECM to the main relay of the relevant lines, show are normal.
3. With an oscilloscope to measure the crankshaft position sensor data found in the car sensor waveform and normal vehicles have obvious differences. Failure of the car crankshaft waveform measured the number of teeth for 57 teeth and found that there is a significant lack of teeth phenomenon.Normal vehicle waveform crankshaft rotation of a circle waveform tooth number of 58 teeth and evenly arranged.
4. Disassemble the starter to observe the signal wheel teeth state, found that one of the teeth of the signal wheel teeth have been deformed, the signal wheel teeth and the gap between the sensor is too large.

Solutions

Replace the flywheel

fault resolution

1. This car uses a Hall crankshaft position sensor, using the principle of the Hall effect, generating the crankshaft angle corresponding to the voltage pulse signal. It is the use of gear teeth to change the strength of the magnetic field through the Hall element, so that the Hall element produces pulses of Hall voltage signals, amplified by the shaping of the crankshaft position sensor output signal to the ECM, the car due to the signal gear teeth have a section of the deformation when turned to the sensor position when the crankshaft position sensor does not produce a difference in the voltage, whenever the signal gear teeth rotated to the place there is no output of voltage signals to lead to the fault lights on. The malfunction lamp lights up.
2. In the maintenance and inspection process is recommended to use more diagnostic equipment such as oscilloscopes, etc., the car using oscilloscopes to detect the waveform can be very clear to see the location of the fault, reduce the scope of the fault, saving maintenance time.