Truck maintenance relies on theory, experience and skills, and focuses on physical and mental strength. But is that enough? These are far from enough. You also need to have strong learning ability and analysis ability, so that you can be comfortable in maintenance. This issue will show you a fault case that needs strong “analysis ability” to be solved.
1. Use a diagnostic expert to read the fault code. According to the above fault code, when p0336 – crankshaft signal interference or signal loss fault code is reported, it will lead to insufficient engine power; When p0089 – pressure limiting valve is opened and the fault code is reported, it will lead to insufficient power and engine speed limit.
Tip: when the engine has a synchronization related fault, it may cause the ECU to restart. After the ECU restarts (the metering unit is normally open), the pressure limiting valve will open and report p0089 fault. Therefore, the two fault codes p0036 and p0089 are related to each other. When troubleshooting, repair the first one first.
2. Conduct in-situ test run and observe the data flow and corresponding fault codes.
In terms of data flow, the engine synchronization is normal, and the relevant sensor data is also normal. No problems related to data flow are found.
Clear the relevant historical fault codes. During the in-situ test run, the display system is normal and there is no fault code.
In other words, the fault did not reappear during the in-situ test run. Now it can be determined that the fault is an accidental fault. Next, it is planned to test run.
Tip: for this kind of accidental fault, we must find a way to make the fault reappear, so as to find the fault point faster and more accurately in combination with the fault phenomenon.
3. During the road test, when the heavy load is accelerated, the fault lamp is on, the fault reappears, and the fault code is read as shown in the figure below:
It can be seen from the above figure that two current faults are reported. First, check p0036 – crankshaft signal interference or signal loss fault.
The fault is generally caused by the following reasons:
● harness fault
● sensor failure
● signal panel fault
● installation clearance
● ECU Hardware or software problems
It is initially suspected that the crankshaft sensor and sensor harness are faulty.
4. Replace the crankshaft sensor and and the crankshaft sensor harness flying wire.
After replacement, it went out for test run, and the fault remained the same. Now it is suspected that there is a problem with the signal panel. Use the oscilloscope to read the signal panel information.
5. Use an oscilloscope to read the synchronous timing waveform.
There is no problem reading waveform with oscilloscope, indicating that there is no problem with signal panel.
Through the current troubleshooting steps, it can be determined that there is no problem with the crankshaft sensor, the harness and the signal panel. Since the fault occurred during heavy load, it is suspected that the gap between the crankshaft sensor and the signal panel changed during heavy load, resulting in p0036 – crankshaft signal interference or signal loss.
6. Remove the transmission and check the flywheel disc alignment.
Through inspection, it is found that the flywheel disc rotates well and the clearance is normal.
The clearance is normal, the signal panel is normal, the sensor is normal, and the harness is normal. There are ECU software and hardware left. The next step is to replace the ECU.
7. Replace the ECU and let the master go for a road test, or report the fault during heavy load acceleration.
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