After a long-term research and analysis on the quality of the vehicle pipeline, the reasons for the quality of the vehicle pipeline problems are mainly three: design, there is unreasonableness in the layout design of the vehicle wiring harness; parts quality, the size of the wiring harness parts provided by the outsourcing supplier does not meet the design requirements; the vehicle assembly integration, wiring harness and other pipeline parts are not assembled in place. 2.1 There is unreasonableness in the layout design of the vehicle harness If there is unreasonableness in the layout design of the whole vehicle harness, it is easy to cause interference between the harness and other parts, which leads to potential pipeline quality risks and induces the quality problems of the whole vehicle pipeline after sale. The following two unreasonable situations are common in the design of the wiring harness: ① The branch length of the wiring harness is unreasonably designed, too long or too short, causing interference between the wiring harness and the surrounding parts, leading to wear and tear of the wiring harness or other pipes. ②The outer wrapping bellows of the harness is not selected reasonably, the diameter is too thick, causing interference between the harness and the surrounding parts, causing the harness or other pipeline wear. As shown in Figure 3a, the EPS branch of the engine harness of an aftermarket model interferes with the transmission case, causing the harness to wear out and causing the power steering function to fail. As shown in Figure 3, A and B are two pegs on the EPS harness branch, peg A fixes one end of the harness to the EPS, and peg B fixes the other end of the harness to the engine.

Analysis of the causes of the harness wear: ① harness A-B section design definition is too long, and the fixed point A for offset pegs, does not have anti-rotation function, EPS harness branch in the limit of the case and the transmission case interference; ② engine and EPS relative motion, the harness belongs to the cross-motion area arrangement, due to dynamic friction between the harness and the transmission case, resulting in harness breakage, and ultimately triggered the vehicle electric power steering Function failure. Design optimization: shorten the length of the A-B section of the wire harness by 15 mm to ensure that the wire harness does not interfere with the transmission case during extreme motion, and increase the wear-resistant bellows protection on the outside of the wire harness.

Figure 4 shows the engine wiring harness injection rail branch and fuel pipe interference. The arrangement here has a small space and the outer protection bellows of the harness has a thicker diameter, causing interference with the fuel pipe. Due to the vibration of the engine, there is a potential risk of abrasion of the fuel pipe. After analysis, the diameter of the harness here is much smaller than the inner diameter of the bellows, and the diameter of the harness bellows is too thick, causing interference with the fuel pipe. The analysis assessed that it would be more appropriate to use a smaller outer diameter (Ф23.8 mm) bellows for this section of the harness, which could meet the harness protection requirements and ensure sufficient safety distance between the harness and the fuel pipe.

2.2 wire harness and other outsourcing parts manufacturing quality problems supplier outsourcing wire harness and other pipe parts manufacturing quality is poor, will also lead to the quality of the vehicle pipeline problems. At present, the production process of wiring harness is mainly done by hand, and it is difficult to ensure the consistency of wiring harness production quality because of the great difference in manual operation. Harness production quality mainly refers to the size of the harness provided by the supplier does not meet the design requirements, commonly manifested as follows: ① harness length beyond the design tolerance range; ② harness branch out of the line angle and model design does not match; ③ harness fixed with the direction of the nail and model design does not match; ④ harness outside the package is not good, resulting in exposed wires. Generally speaking, for the production of wiring harness, in addition to the internal control standards of suppliers, the vehicle manufacturers will develop more stringent technical specifications requirements. Table 1 lists some of the wiring harness branch length tolerance definitions for reference. Harness branch angle regulations: the maximum angle between the branch's natural state rotatable angle and the digital model angle does not exceed 22°.
2.3 The whole vehicle wiring harness and other parts assembly is not in place the whole vehicle pipeline parts assembly is not in place, wrong installation, omission, etc., the same will cause the whole vehicle pipeline quality problems. Common assembly problems are: ① harness pins are installed in the wrong position, causing interference and other problems; ② fixed harness towards the bracket is not assembled in place, resulting in harness and surrounding parts interference; ③ assembly is not organized according to the required gestures harness direction, causing harness interference.