After Just Repairing The Urea Pump, The Post-Treatment... 3
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After Just Repairing The Urea Pump, The Post-Treatment Light Is On Again. What Should I Do?

The after-treatment light of the vehicle suddenly came on, and the driver thought that it had just been on last month, which cost more than 1000. Why is it on again now?

This is a Shaanxi Automobile Delong X3000, which uses Weichai wp15 engine and Weichai independent board. The post-treatment is also Weichai independent board. Last month, the urea pump was blocked due to impurities in it. The urea system was replaced and cleaned.


Our master Guo had just finished breakfast today and was ready to stretch. At this time, he saw the faulty car coming slowly. Then start making money! The driver described that the fault light of this vehicle is on and the torque is limited.
As long as the vehicle fault light is on, first check the fault code with the diagnostic instrument, which is the maintenance idea. I don’t even know the fault code. Which direction should I repair?

Fault code of post-treatment:

  • Use the diagnostic instrument (machinist C80) to check that there are four current fault codes, namely p0042 exhaust brake disc valve open circuit, p0052 urea tank heating solenoid valve open circuit, p0118 urea tank liquid level measurement value is too high No outbound links were found. Link out to external resources, p0131 urea tank liquid level is low, and others are post-processing related historical fault codes!
    Analyze the fault codes. Don’t worry after seeing the fault codes. There may be more than ten fault codes in a car. We need to select the fault codes related to the fault phenomenon from these fault codes and give priority to maintenance.

Analyze fault code of post-treatment:

  • Although the open circuit of p0042 exhaust brake disc valve is a current fault, it does not affect urea consumption and torque limit. On the contrary, p0052 / p0118 / p0131 are the current faults of post-processing and the historical faults related to post-processing. These post-processing faults are the source of the faults that do not consume urea and torque limit. Analyze relevant post-processing faults, whether current faults or historical faults, all point to the post-processing system.

Troubleshooting process of post-treatment:

  • 1. Use the detector to enter the DCU (post-treatment control module) system and find that it is unable to enter, but the ECU (engine control module) can enter, indicating that the can network of the whole vehicle can communicate. The post-treatment module is not detected after scanning with the “can bus analysis” in the electronic control system of the diagnostic instrument, which indicates that the communication between the DCU module and the can network of the whole vehicle has been lost.
  • Look up the circuit diagram and measure the DCU communication line. No abnormality is found. Considering that if there is a problem with DCU power on, even if the communication line is normal, it is also unable to communicate when DCU does not work, so connect and measure the voltage of the upper wire of DCU. When finding the upper wire of dcu-57, it is found that there is only 10V voltage, and the normal power on voltage of DCU is 24V.
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  •  Check the circuit diagram and find that the K6 (DCU main relay) measuring relay in the post-processing fuse box works normally. The No. 30 power line of the measuring main relay is 24V normal. Considering that the power supply line of the main relay and the main relay are normal, then measure the resistance of No. 87 output terminal and No. 57 power supply terminal of the host relay. After measurement, it is found that the resistance exceeds the normal range. (I forgot to take the photos here for the specific resistance value)
  •  No abnormality was found in this section of harness after skin breaking inspection, so we decided to disassemble the fuse box and deal with it to check whether it was a false connection of wiring terminals. However, we found a lot of corrosion signs at the back of the fuse box after disassembly. After that, communicate with the owner to replace the post-processing fuse box and solve the fault after performing the override test!

Summary of post-treatment:

  • All faults that affect the operation of the post-treatment system will report flash codes. The difference is that some faults are very clear (for example, the heating resistance wire of the urea pump is open circuit), and some faults have a wide range (for example, the pressure building error of the urea pump, which may include the faults of the urea pipeline, urea pump, etc.). On the basis of in-depth understanding of the post-treatment structure, the direction of troubleshooting can be found by reading the fault code;
  • Some faults do not need to be reported immediately or after the start of the cycle. For example, in the process of production and installation in the vehicle factory, it is impossible to avoid inserting, pulling and installing urea nozzles. In order to prevent the vehicle from leaving fault codes before leaving the factory, the relevant faults of urea nozzles are not reported in the early stage of vehicle use;
  • After some faults are repaired, although the flashing light and OBD light will go out immediately, it needs to go through a certain driving cycle or time to clear the historical fault code (required by the Ministry of environmental protection of the people’s Republic of China);
  • Some faults can be detected only during the operation of the post-treatment system. Once the engine is shut down, they will become historical faults and will be reported again during the next post-processing work. For example, the urea pipeline is blocked. When the vehicle is just started, the after-treatment system does not work, so the pipeline detection is not carried out; When the urea pressure is established, check whether the pipeline is blocked before reporting a fault. Once the engine is shut down, the fault disappears.
  • The faults of post-treatment system belong to component faults. It is easy to solve as long as we have a thorough understanding of the working principle and various structures of post-treatment.
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