As we all know, communication failure will bring all kinds of difficult and miscellaneous diseases to the vehicle, such as unable to get on the vehicle, difficult start, insufficient power, etc. the problems mostly appear in the circuit and are difficult to troubleshoot. It is necessary to use professional diagnostic equipment and rich maintenance experience for diagnosis and inspection. Today, let’s take a look at a recent case encountered by the coachman of truck engine.
Model: Shaanxi Automobile X3000
Engine model: WP13 500E501
Emission standard: national five
Computer version model: Weichai independent
Fault phenomenon: the engine and post-processing fault light is on, and the power is insufficient.
Fault code: see Figure
1. There are many engine fault codes read about post-processing DCU fault codes. Entering DCU cannot enter the system.
2. According to the analysis of engine fault code, ECU does not receive the can message from DCU, and DCU cannot enter the diagnostic system. It is suspected that the power supply of DCU module is faulty.
3. Check that there is no 24V voltage at pin 4 of DCU power supply. Check that the fuse of DCU is blown out. After replacing the new fuse, the fuse of key opening door is blown again, indicating that there is a short circuit to ground fault in the line of truck engine.
4. The relevant circuit diagrams are as follows:
5. Check along the harness and find that there is interference between the power supply line and the frame. Peel off the harness binding tape. As expected, the grounding has been worn and there is obvious ablation at this position. As shown in the figure of truck engine:
6. The harness shall be insulated and re fixed, and the fuse shall be replaced to eliminate the fault.
In case of short-circuit fault, focus on the interference part between the harness and the body support. The relative movement between the frame and the harness is often caused by poor driving conditions, resulting in the abrasion of the harness insulation and short circuit to ground.
More and more can lines are used in new models. When ECU reports OBD and DCU related faults, all maintenance masters must enter the post-processing, read the relevant fault codes and analyze the cause of the fault.
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