No Trouble Found Research Articles

The seven-step failure diagnosis in automotive industry

Problem solving (PS) competency has been considered as the key competitive weapon for automotive manufacturers. Correct and reliable diagnosis is considered as the most important challenge in PS process. In this study, the seven-step approach for complex and cross-functional diagnosis has been developed based on the first two steps of universal PS approach. The proposed procedure puts the phenomenon forward prior to the definition of root causes. Obviously, it will speed up the PS process by narrowing the search perimeter. The structured and validated procedure guides the experts to optimize their diagnosis process. The new method was integrated with knowledge management system ‘SW e-Lua’ to transfer the accumulated know-how to the new projects. The key indicators, such as diagnosis performance, lead time, and no trouble found (NTF) ratio, have been developed to improve the efficiency of the new approach. The significant improvements were obtained through three years of implementation. By this way, the competency level of the diagnostic experts could be traced and improved. The factors affecting the complexity and the quality of a diagnosis were proposed and surveyed through OEMs, suppliers and aerospace industries. The structured problem description and the validated phenomenon were defined as the most important factors to narrow down the perimeter of the problem; consequently, they increase the efficiency of the diagnosis process. On the other hand, non-linear interaction of parameters, failure repeatability, and the necessity of advanced diagnostic equipment usage were revealed as the highest impact on the diagnosis complexity.

Fault Diagnostics Using Network Motif Signature


 
 
 In modern vehicles, controls are distributed over multiple Electronic Control Units (ECUs) that are connected through in-vehicle communication networks. Fault diagnostics for such a distributed control system is very challenging, which has resulted in many no-trouble-found (NTF) cases during warranty repairs. To address this problem, we propose a novel network-theoretic approach that detects, identifies, and localizes faults using both the structure of the communication network (topological information) and message flow information. The proposed method not only enables the characterization of normal operation and a-priori known faults across communication networks, which is already beyond the current practice of individual ECU centric diagnostics, but also the diagnostics of unknown or cascading failures emerging from unexpected operational environments.
 
 

Reproduction and Detection of Board-Level Functional Failure

No trouble found (NTF) due to functional failures is a common scenario today in board-level testing at system companies. A component on a board fails during the board-level functional test, but it passes the automatic test equipment (ATE) test when it is returned to the supplier for warranty replacement or service repair. To find the root cause of NTF, we propose an innovative functional test approach and discrete Fourier transform (DFT) methods for the detection of board-level functional failures. These DFT and test methods allow us to reproduce and detect functional failures in a controlled deterministic environment, and provide ATE tests to the supplier for early screening of defective parts. Experiments on an industry design show that the proposed functional scan test with appropriate functional constraints can adequately mimic the functional state space, as measured by appropriate coverage metrics. Experiments also show that most functional failures due to dominant bridging, crosstalk, and delay faults due to power supply noise can be reproduced and detected by functional scan test. We also describe two approaches to enhance the mimicking of the functional state space. The first approach allows us to select a given number of initial states in linear time and functional scan tests resulting from these selected states are used to mimic the functional state space. The second approach is based on controlled state injection.

The “trouble not identified” phenomenon in automotive electronics

In some cases, a failure occurs that cannot be verified, replicated at will, or attributed to a specific failure site, mode, and mechanism. Terms used to describe this phenomenon include trouble not identified (TNI), no trouble found (NTF), cannot duplicate (CND), `re-test ok' (RTOK), no-fault found (NFF), and intermittent malfunctions. This paper discusses the concept, causes, and impact of the “trouble not identified” phenomenon on the automotive electronics industry. A case study is presented to clarify the issues. The key conclusion is that a manufacturer should assume that all field returns are field failures, unless some alternative reason can be verified. In fact, any company that produces a safety or emission regulated product should assume that every complaint or return of that product is a failure, and take on full responsibility for ascertaining the root cause. It must not be assumed that a returned module that passes tests associated with an engineering specification is good.

An investigation of ‘cannot duplicate’ failures

Various terms such as ‘cannot duplicate (CND)’, ‘re-test OK (RTOK)’, ‘no fault indicated (NFI)’, ‘no fault found (NFF)’, and ‘no trouble found (NTF)’, are used to describe the inability to replicate field failures during laboratory assessment. This paper uses CND to refer to all such failures. CND failures can make up more than 85% of all observed field failures in avionics and account for more than 90% of all maintenance costs. These statistics can be attributed to a limited understanding of root cause failure characteristics of complex systems, inappropriate means of diagnosing the condition of the system, and the inability to duplicate the field conditions in the laboratory. This paper addresses CND issues with reference to research carried out on samples of an electronics board used as the seat-back processor modules on board the Boeing 777. The boards were monitored continuously using existing on-board comprehensive built-in test equipment. It was found that the hot temperature operating limits of the board decreased by up to 70°C during highly accelerated environmental stress. Furthermore, improperly seated connectors were found to result in spurious component failure reports from the built-in test equipment. This paper suggests that the observed drift in operating limit and connector issues are two likely root causes of CND failures and makes recommendations for addressing them. © Crown Copyright 1998. Reproduced with the permission of the Controller of Her Majesty's Stationery Office.

An investigation of ‘cannot duplicate’ failures

Various terms such as ‘cannot duplicate (CND)’, ‘re-test OK (RTOK)’, ‘no fault indicated (NFI)’, ‘no fault found (NFF)’, and ‘no trouble found (NTF)’, are used to describe the inability to replicate field failures during laboratory assessment. This paper uses CND to refer to all such failures. CND failures can make up more than 85% of all observed field failures in avionics and account for more than 90% of all maintenance costs. These statistics can be attributed to a limited understanding of root cause failure characteristics of complex systems, inappropriate means of diagnosing the condition of the system, and the inability to duplicate the field conditions in the laboratory. This paper addresses CND issues with reference to research carried out on samples of an electronics board used as the seat-back processor modules on board the Boeing 777. The boards were monitored continuously using existing on-board comprehensive built-in test equipment. It was found that the hot temperature operating limits of the board decreased by up to 70°C during highly accelerated environmental stress. Furthermore, improperly seated connectors were found to result in spurious component failure reports from the built-in test equipment. This paper suggests that the observed drift in operating limit and connector issues are two likely root causes of CND failures and makes recommendations for addressing them. © Crown Copyright 1998. Reproduced with the permission of the Controller of Her Majesty's Stationery Office.