Wire Harness Common Fault Analysis

- Sep 21, 2017-

Failure analysis

Wiring harness, ablation of the wiring harness, ablation is the engine harness "the most dangerous" of a failure mode, serious can lead to fire car. There are many reasons for the burning of the engine harness, ablation of the following five kinds of analysis.

1) from the heat radiation source too close, resulting in rapid aging wiring harness.

2) around the high temperature gas leakage, wiring harness ambient temperature exceeds the material can withstand the temperature range.

3) the environment is relatively closed, less air convection, mainly rely on radiation heat, cooling speed is slow.

4) circuit overload, leading to intense heat and burn the external insulation sleeve.

5) did not do the wiring harness fixed, protective measures. Harness in the engine, exhaust pipe, water pipes and other heat near, often due to the lack of wire harness clip was hot baked, or even scorched, resulting in electrical equipment can not work properly.

Failure phenomenon: a steam from the General Motors Wuling Automobile Co., Ltd. production Wuling Hongguang 5 car, configuration 1.5 L engine, mileage 4 million km. After the vehicle dismantling the vehicle after the scene to confirm the parts, found that the exhaust system around the engine wiring harness speed sensor branch was scorched, harness outer corrugated pipe cracked off, check to confirm the high temperature aging caused.

Check the results: the damaged wire harness in the normal heat radiation distance range (measured in other models on the same car), and the vehicle in the vicinity of the damaged wire harness ternary catalyst and exhaust pipe connection occurs loose bolt Of the leak failure.

Analysis of the reasons: the exclusion is the harness branch of their own design, quality problems, changes in the external environment - high temperature gas leakage is the main cause of harness burning.

Corrective measures to analyze the causes of high temperature gas leaks and find reliable solutions.

Failure Analysis 2: Harness wear

One of the most important reasons for the wear of the engine harness is interference with the surrounding parts. The engine harness is arranged in a wide area and is a variant, and the probability of interference between the harness and the peripheral parts is greater than that of other engine components.

There are many reasons for the interference between the wiring harness and the peripheral parts. If the harness branch design is too long, the harness margin is too large to interfere with the peripheral parts. The assembly process does not meet the design requirements. The layout is unreasonable, the space is insufficient or the fixed point is missing, Too close to lead to interference.

Symptom 2: A Wuling Automobile Co., Ltd. produced by SAIC-Wuling Automobile Co., Ltd., equipped with 1.5 L engine, mileage of 1.8 million km, the inspectors found the engine wiring harness crankshaft position sensor branch and clutch There is interference in the pump mounting bracket, and there is a wear in the harness branch.

Auto repair master micro letter: 2900184521

Inspection results: The engineer went to the test site to confirm that the engine harness branch was engaged with the clutch cylinder mounting support and that there was no fixed point within 10 mm of the interference area.

Cause Analysis: The engine harness branch is arranged at the upper right of the clutch cylinder bearing, and there is no fixed, the latter test again found that there is friction between the two vehicles in the process of interference.

Corrective measures: increase the two wiring harness soft clip to fix the engine harness branch here.

Failure Analysis 3: Harness Break

Harness break can lead to the circuit break This common vehicle failure mode, the reason for the wiring harness can be simply listed as the following 3 points:

① harness branch design is too short;

② wiring harness manufacturing is not standardized;

③ twisted harness when assembled.

Symptom: a Wuling GM Wuling Automobile Co., Ltd. produced Wuling Hongguang S-like car, with 1.2 L engine, mileage of 3.3 million km, the test staff found that vehicles running frequent speedometer indicates the speed is zero, odometer Indicating that the mileage is too small (intermittent self-normal) failure.

Check the results of the test personnel to replace the measurement of vehicle speed sensors and instrumentation for temporary troubleshooting, found that the fault still exists, the harness engineer to the field field troubleshooting, in the investigation of the speed sensor power supply, ground situation, found that the speed sensor power supply voltage of 2.5 V, does not meet the normal work requirements.

Analysis of the reasons: wire harness engineers found that the engine wiring harness speed sensor power cord junctions are not bandaged, was exposed to damage, resulting in wire resistance is too large, speed sensor power supply voltage is too low, can not work properly.

Rectification measures: increase the quality of the engine harness management, the harness product sampling methods, the number of times to make the appropriate adjustments.

Failure Analysis 4: Poor contact

Harness assembly connector bad is a common engine harness failure mode, to promote the cause of this failure can be simply divided into the following three kinds:

① jacket manufacturing in the quality of the problem;

② plating set unreasonable, the terminal oxidation too fast;

③ assembly process of human factors to make the connector terminal deformation.

Failure phenomenon 4: a steam from the Wuling Automobile Co., Ltd. produced Wuling Hongguang right rudder-like car, with Euro Ⅳ1.3 diesel engine, mileage 2.6 million km, in the test found that the engine can not start. After the test personnel re-align the rail pressure control valve sensor connector, the engine can start normally, but the engine is working properly, the fault reappears.

Check the results: harness engineers to the scene check found that the engine wiring harness pressure control valve sensor connector internal terminal has a slight ablation, the lack of locking pieces of the plug, as shown in Figure 4.

Cause analysis: lack of locking pieces on the jacket, the terminal can move in the jacket, resulting in harness and rail pressure control valve sensor docking bad.

Rectification measures: increase the quality of the plug-in supplier of product quality control, and strive to full product inspection.

Failure analysis 5

Leading to harness connector damage common factors First, product quality problems, factors for the two assembly factors, assembly factors are mostly caused by violent operations.

Symptom 5: a Wuling GM Wuling Automobile Co., Ltd. production of Wuling light lengthened car prototype, with 1.2L engine, mileage of 2.8 million km, the test personnel in the daily inspection of vehicles found that the engine failure lights often bright.

Check the results: X431 with a diagnostic device to remove the fault code after two days, found the fault again, read the fault code P0075, found that the engine intake valve circuit failure, the test staff found that the engine harness access VVT valve and intake VVT valve can not be reliably docked.

Analysis of the reasons: the fault pieces from the car on the dismantling back to the harness engineer, through the fault pieces and the normal comparison found: before docking, the normal part of the secondary lock in the non-locking state, and the fault is in the locked state, see Figure 5. In the non-assembled state it is difficult to lock the secondary lock, the violent operation causes the secondary lock to be locked before docking.

Corrective measures: In the car assembly process marked with a two-stage plug with the disassembly instructions.

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