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How To Solve The Difficulty Of Starting The Vehicle Come And Learn

How To Solve The Difficulty Of Starting The Vehicle Come And Learn

When it comes to the difficulty of vehicle starting, many masters will think of the problem of synchronous timing. Vehicle synchronization related faults are common faults of starting the vehicle.

In traditional maintenance, it is often a decoder plus a set of wrenches to solve the problem, but is it OK to repair the synchronization fault in the traditional way of starting the vehicle?

I believe that many masters who have repaired the synchronization problem know the answer, so masters who have not repaired this fault don’t have to worry. Today, we’ll learn about synchronization timing with questions.

The driver of a Weichai Guowu fault vehicle was asked that the fault phenomenon was that the vehicle was occasionally difficult to start and would suddenly shut down during operation.

Step 1: Go Out For Commissioning Due To Accidental Failure Of Starting The Vehicle

First of all, there is an accidental fault, so don’t think about it. Go out for a test run to see when the fault light turns on and what fault code will be reported when it turns on of starting the vehicle?

After a period of time, when the fault light is on, read the fault code as of starting the vehicle:

P0335: no crankshaft signal;

P0340: no camshaft signal.

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Step 2: Check The Synchronization Signal

Although the fault was cleared, we saved the fault screenshot at that time. These two synchronization related fault codes were shared with you in previous articles. In fact, the reason is that the synchronization signal is abnormal, so it will be difficult to start the vehicle of starting the vehicle.

The reason for flameout during vehicle driving is also that the ECU calculates the wrong fuel injection time due to abnormal synchronization signal, resulting in flameout during vehicle operation of starting the vehicle.

Now that we have found the fault point, we will focus on the synchronization signal. How do we usually check this kind of fault? (the teacher is going to knock on the blackboard!) of starting the vehicle.

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[Key] Four Key Points Of Synchronization Signal Inspection:

1. Check whether the crankshaft camshaft harness is normal, open circuit, short circuit, etc of starting the vehicle;

2. Check whether the crankshaft and camshaft sensor connectors and corresponding terminals are normal, whether there is rust, needle withdrawal, etc of starting the vehicle;

3. Check whether the resistance of crankshaft and camshaft sensor is normal, which should be within (860 ± 86 Ohm) under normal conditions;

4. Connect the oscilloscope to check whether the signal waveform is normal when the crankshaft and camshaft are idling.

Through the 4-point inspection, it is found that the sensor resistance is within the normal range, there is no obvious short circuit or open circuit in the harness, and there is no obvious rust and needle withdrawal in the sensor plug. Only through the oscilloscope can we see whether the sensor waveform is normal!

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The Yellow waveform in the figure above is the waveform of the crankshaft position sensor collected by the oscilloscope. It can be seen from the waveform that the waveform collected by the sensor is type 60-2 (there are two missing teeth on the crankshaft signal plate). The waveform is stable during idle operation, and there is no obvious interference.

So why does such a smooth waveform report a fault without crankshaft signal? So continue to collect camshaft signals for observation.

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It can be seen from the camshaft waveform that the camshaft is 6 + 1 type (one multi empty). During idle operation, the waveform is stable without obvious interference, and the waveform is normal.

Through the inspection of the oscilloscope, it is found that the signals detected by the crankshaft camshaft position sensor are normal. Why does the vehicle stall occasionally?

The maintenance has not found the fault point up to now, but the fault really exists. It must be that the inspection is not in place. Continue to connect the oscilloscope, look at the waveform while driving the car, and shake the sensor harness. The harness from crankshaft camshaft position sensor harness to ECU is relatively short.

There is no jumper plug, and the harness is twisted shielded wire, so the harness interference rarely occurs. When we continued to check with questions, we shook the harness for a period of time and found that there was a deviation in the synchronization waveform!

It can be seen from the video that when shaking the harness, the crankshaft signal running smoothly has obvious interference. Here, the real fault point has slowly surfaced.

Step 3: Check The Crankshaft Position Sensor

Since there will be waveform deviation due to shaking, continue to check along the harness, but no obvious abnormality is found. Finally, the target point is placed at the plug of the crankshaft position sensor.

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It can be seen from the figure that the clamping pieces are separated greatly and cannot be clamped tightly at the plug insert of the crankshaft position sensor.

Therefore, when the vehicle runs on bumpy road conditions, it will stall or run unstable. Replace the plug and continue to go out for test run!

Step 4: Commissioning And Troubleshooting

After commissioning for a period of time, the fault did not appear. This fault is eliminated! The difficulty of this fault is that the fault occurs occasionally and there is no problem when the oscilloscope reads the waveform normally for the first time.

However, as long as there is a fault phenomenon, there must be a fault cause. For example, when encountering an occasional fault, the vehicle usually occurs in bumps or some special road conditions, so we can try to simulate the current road conditions (artificially shaking the harness plug).

Fault Summary

  • Question 1: why does the vehicle feel frustrated when it loses the crankshaft signal?
  • A: under the joint action of crankshaft and camshaft, the ECU is given the current synchronization state, that is, fuel injection time. When there is a problem with the fuel injection time, the vehicle will definitely feel frustrated or stall.
  • Question 2: what happens when a synchronization signal is missing?
  • Answer: ECU judges the angle phase (also known as cylinder judgment) of diesel engine operation according to the phase relationship between crankshaft signal plate and camshaft signal plate of electronically controlled diesel engine to calculate the speed of diesel engine. And the fuel injection can be started only after the cylinder judgment is successful. There are three common states: normal mode, backup mode 1 and backup mode 2.
  • A. Normal mode (crankshaft / camshaft sensors are normal)
  • During the starting process, when the crankshaft signal and camshaft signal are normal, ECU judges the cylinder in combination with the judgment of crankshaft missing teeth and camshaft multi teeth. The cylinder judging process is fast and reliable.
  • B. Backup mode 1 (camshaft sensor only, crankshaft sensor signal lost)
  • During the starting process, when there is only camshaft signal, the ECU determines the correct phase of the current diesel engine by detecting the cylinder teeth (excess teeth in front of the first cylinder), so as to inject according to the correct injection timing.
  • C. Backup mode 2 (crankshaft sensor only, camshaft sensor signal lost)
  • In the process of starting, when there is only crankshaft signal, when ECU detects a missing tooth, it is speculated that the diesel engine is before the top dead center of the first cylinder.
  • According to the assumed angle phase, when the engine speed exceeds a certain threshold, it can be judged that the phase is correct, so as to judge the success of the cylinder; If there is no fire sign of speed increase, the missing teeth will be detected again, and one-phase fuel injection will be assumed again to judge the cylinder until the cylinder is judged successfully.

Fault Development (Difficulty Of The Article)

How Does The Ecu Know The Position Of The Engine?

A: two concepts “physical zero” and “software zero” are involved here. The zero position we say generally refers to the top dead center of one cylinder compression.

Physical zero is the current position of the engine determined according to the relative position of the engine crankshaft and camshaft; Software zero position is to obtain the current position of the engine through software calculation according to the signals of crankshaft position sensor and camshaft position sensor.

How does the software zero get the engine position? Let’s talk about it briefly.

The signal panel of crankshaft position sensor generally has 60-2 teeth, of which 2 are missing teeth; The signal panel of camshaft position sensor is usually single tooth and Z + 1 tooth.

During the operation of the engine, the distance between the end face of the signal disc teeth and the sensor probe will change. The sensor will induce sinusoidal waveform or square wave according to magnetoelectric effect or Hall effect and transmit it to ECU for analysis and processing.

According to this waveform signal, ECU can judge the current engine position and further determine the injection time.

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Working principle and troubleshooting of Bosch 315 magnetoelectric position sensor


A: the magnetoelectric sensor uses the principle of electromagnetic induction to convert the input motion speed into the induced potential output in the coil.


It directly converts the mechanical energy of the measured object into electrical signal output without external power supply. It is a typical passive sensor.


The output of the sensor can be detected by oscilloscope. The following small track gives several typical fault waveforms as a reference!


Waveform of crankshaft position sensor collected during idle operation

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  • If the waveform above is collected at a certain speed, it indicates that there is foreign matter at the sensor probe! (★ highlight)
  • 3. Working principle and troubleshooting of hall position sensor
  • Hall effect is a kind of electromagnetic effect. When the current passes through the semiconductor perpendicular to the external magnetic field, the carrier deflects, and an additional electric field will be generated perpendicular to the direction of the current and magnetic field, resulting in a potential difference at both ends of the semiconductor.
  • This phenomenon is the Hall effect, and this potential difference is also known as the Hall potential difference. The simple understanding is that when a signal tooth is turned, the signal voltage will be reversed.
  • The output of the sensor can be detected by oscilloscope. The following track will show you the signal waveform:
  • Signal waveform of hall crankshaft position sensor collected during idle operation
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