Root cause analysis of field failure concern for improvement

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME
232
ROOT CAUSE ANALYSIS OF FIELD FAILURE CONCERN FOR
IMPROVEMENT IN DURABILITY OF VEHICLE SYSTEM
A. D. Lagad1
, Dr. K. H. Inamdar2
1
Department of Mechanical Engineering,
Walchand College of Engineering, Sangli, Maharashtra, India,
2
Department of Mechanical Engineering,
Walchand College of Engineering, Sangli, Maharashtra, India
ABSTRACT
Durability and reliability of an automobile are equally important from industry as well
as customer point of view. Automotive industries are still riddled with significant warranty
costs that incur due to premature failure of their products in the customer hands. The key to
reduce the design and development expenses and warranty expenses is to subject the product
for reliability and/or durability tests for failure modes investigation. Design of the vehicle
components must be adapted as accurately as possible to the operating conditions. In order to
achieve these goals, durability tests are performed through a combination of physical testing,
on road at a proving ground test track, and using a servo-hydraulic road test simulator in
laboratory. In this study, root cause analysis is carried out for bonnet cable failure in vehicle
model of an automotive industry. Various possible causes are identified using fishbone
diagram, why-why analysis is carried to find root cause and solution is proposed. Modified
design of hood latch reduced operating efforts for hood latch and avoided bonnet cable
failure.
Keywords: Durability, Reliability, Root cause analysis, Fishbone diagram.
1. INTRODUCTION
In automotive industry, vehicle safety and product quality are prime factors on which
automotive manufacturers give significant attention. During vehicle manufacturing, defects
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ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 4, Issue 3, May - June (2013), pp. 232-243
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arise during manufacturing, assembly and other processes. For continuous quality
improvement and customer satisfaction, plant quality functions are planned, integrated and
executed to detect these defects and make action plans, preventive measures to resolve them.
Currently, automotive industries are dedicating a lot of attention to improve product
quality, durability and reliability already in a virtual simulation environment. A major issue
that designers and manufacturers in this field have to face is to improve vehicle lifetime [1,2].
Durability and reliability of a vehicle are equally important from a customer point of view.
Automotive industries are still riddled with significant warranty costs that incur due to
premature failure of their products in the customer hands [3]. Vehicle manufacturers discover
issues through their own vehicle tests, inspection procedures, or information gathering [2]. In
order to achieve improved durability and reduced warranty costs, durability tests are
performed through a combination of physical testing, on road at a proving ground test track,
and using a servo-hydraulic road test simulator in laboratory [4].
Modern vehicles exhibit a variety of performance, safety and comfort features in
which they fundamentally differ from previous models. Durability and reliability in vehicle
components are prime considerations for successful functioning of vehicles in all aspects
mentioned above [5, 6].
In this study, root cause analysis is carried out for bonnet cable failure in vehicle
model of an automotive industry and solution is implemented accordingly. Various finished
vehicle audits performed in automotive industry considered are ANOVA-C (Advanced New
Overall Vehicle Audit), GD (Global Demerit) test and Durability ANOVA-C. The purpose of
Durability ANOVA-C is to check and capture data on internal/known customer vehicles
periodically to get early feedback on field failure and make action planning [7,8].
2. CONCERN RESOLUTION- BONNET CABLE FAILURE
Concern identified and considered for resolution is ‘High Operational Effort for Hood
Latch Release Lever’ which results in bonnet cable failure. This concern is identified during
durability ANOVA-C and GD audit. Effort readings taken on internal customers’ vehicle are
shown in table 1. Specifications are 40-80 N. Table 2 shows hood latch release lever effort
readings for 60 Ready for Inspection (RFI) vehicles. Higher operational efforts are observed
for some vehicles.
Table 1: Hood latch release lever efforts for internal customers
Customer
Lower Limit
(N)
Upper Limit
(N)
Phase 1
(N)
Phase 2
(N)
Phase 3
(N)
1 40 80 55 110 122
2 40 80 55 110 85
3 40 80 69 72 75
4 40 80 76 98 100
5 40 80 99 108 105

234
Table 2: Hood latch release lever effort readings for 60 vehicles
Sr. No
Effort
(N)
Sr. No
Effort
(N)
Sr. No
Effort
(N)
Sr. No
Effort
(N)
1 73 16 64.9 31 71.3 46 70
2 67.8 17 69.7 32 69.3 47 74.3
3 56.8 18 54.6 33 58.4 48 71.9
4 59.3 19 64.4 34 66.7 49 76.5
5 78.1 20 86.1 35 77.8 50 62.8
6 76.1 21 61.4 36 74.3 51 64.1
7 78 22 78 37 55.4 52 64.4
8 66.9 23 64 38 67.3 53 71.3
9 63.3 24 80.6 39 67.8 54 69.1
10 70.8 25 71.2 40 66.1 55 64.6
11 69.4 26 65.2 41 77.5 56 66.1
12 77.3 27 59.3 42 70.6 57 72.7
13 74.2 28 63.2 43 62 58 71.4
14 66.1 29 73.1 44 72.2 59 100
15 77.4 30 76.1 45 77.5 60 69.2
Bonnet cable failure is third in the list of significant field failure concerns as shown
in pareto diagram in fig. 1. Analysis is already carried out for first two concerns.
2.1 Process Flow for Bonnet Cable and Lock assembly
Bonnet cable and bonnet lock are fitted and assembled on assembly line in TCF. Steps
involved in this process are mentioned below,
1.Bonnet cable fitment is done on body with grommet and plugs (Trim Line).
2.Bonnet cable bracket is fitted on cockpit (Trim Line).
3.Hook of bonnet cable is assembled with bottom side hood latch (Underbody Line)
4.Bottom side hood latch is fitted on front grill upper body panel with 3 bolts by giving full
torque (Underbody line)
5.Loose mounting of top side hood latch on bonnet bottom side with 2 bolts by pre torque.
(Final line)
6.Alignment of bonnet as well as both hood latch parts. Tightening of top side hood latch by
giving full torque to bolts (Final line)

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May
Fig. 1 Pareto diagram for significant field failure concerns
Alignment process is done in following steps,
1.Alignment of hood by retightening hinges (both locks are in loose condition).
2.Gap & Flushness corrected by giving jerk to the hood.
3.Bonnet is locked first time.
4.Opening of bonnet by giving slight stroke to hood with mallet first
due to stuck. Top side lock assembly is again aligned with respect to bottom side lock
assembly.
5.Full tightening of the both hood lock assemblies (body side & bonnet side)
6.Again bonnet is locked & opened 2 to 3 times.
Fig. 2 shows hood latch assembly on vehicle
(b)
Fig. 2 (a) Hood latch assembly on vehicle
6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME
235
Pareto diagram for significant field failure concerns
Alignment process is done in following steps,
ent of hood by retightening hinges (both locks are in loose condition).
Gap & Flushness corrected by giving jerk to the hood.
Opening of bonnet by giving slight stroke to hood with mallet first time if it is not opened
stuck. Top side lock assembly is again aligned with respect to bottom side lock
Full tightening of the both hood lock assemblies (body side & bonnet side)
Again bonnet is locked & opened 2 to 3 times.
shows hood latch assembly on vehicle as well as top and bottom hood latch.
(a)
(b) (C)
Hood latch assembly on vehicle (b) Top side hood latch (c) Bottom si
hood latch
June (2013) © IAEME
it is not opened
stuck. Top side lock assembly is again aligned with respect to bottom side lock
s well as top and bottom hood latch.
Bottom side

236
3. ROOT CAUSE ANALYSIS
After brainstorming, various possible causes contributing to bonnet cable failure are
enlisted. Cause and effect diagram (Fishbone diagram) by using relevant possible causes
identified in brainstorming is shown in fig. 3. Probable causes for bonnet cable failure are
highlighted in figure.
Fig. 3 Cause and effect diagram for bonnet cable failure
3.1 Verification of probable causes
1. Damage to cable while fitment:
i. Fitment process is observed on assembly line.
ii. No damage is observed to cable while fitment
iii. Remark: Invalid
2. Improper cable assembly:
i. Standard operation procedure is followed during cable assembly.
ii. No abnormalities found during cable fitment on body as well as cable assembly with
cockpit and hood latch.
3. Improper cable routine:
i. Bonnet cable routine is observed from release lever end to cable hook end during
fitment, also on finished vehicles
ii. Cable routine was found ok in vehicles. All clips were found on position.

237
iii. Cable routine found ok in vehicles for which higher efforts reported to operate hood
latch release lever
iv. Remark: Invalid
4. Improper alignment of bonnet as well as latch-striker:
i. Alignment is done as per standard operation procedure.
ii. Gaps are measured for bonnet on finished vehicles and alignment found ok.
iii. However, during first locking-unlocking operation in alignment process, cable failure
incidences were observed on final line
iv. As alignment is done in 2-3 attempts by operator judgment- chances that striker gets
stuck in latch in first cycle.
v. Remark: Valid
5. Nut runner not applying required torque/ bolt looseness:
i. Nut runner calibration done as per scheduled frequency
ii. Bolts used for tightening of both latch and striker were checked on finished vehicles for
looseness- Found ok
iii. Torque is measured on finished vehicles, also on vehicles for which higher efforts
reported- torque found as per specification.
iv. Remark: Invalid
6. Deviation of cable length from required length:
i. Bonnet cable length is measured for cables in storage area at side of assembly line
ii. No variation in cable length, length found as per specifications
7. Cracks on cable flap or bracket:
i. Bonnet cables were examined visually for any cracks or damages to cable flap or
bracket
ii. No cracks or damage observed
8. Less thickness for cable flap or bracket:
i. Previous actions: Bracket wall thickness increased by 1.2 mm, Reinforcement added to
flap
ii. Cable flap and bracket thickness measured- Found ok as per modified dimensions
9. Bottom hood latch spring has more stiffness:
i. Parameters such as free length, number of turns, coil diameter contributing spring
stiffness were checked for bottom hood latch spring.
ii. No variation in stiffness- Found ok
10. Cable routine disturbed:
i. Cable routine observed in RFI area, also on customer vehicles during dealer visit.
ii. Cable clips were ensured for position (not fallen)

iii. No abnormalities found
iv. Remark: Invalid
11. Bonnet as well as latch-striker alignment getting disturbed over usage of ve
i. Bonnet alignment observed, gap measurements done and bonnet efforts were taken on
customer vehicles during dealer visit
ii. Gap variation is observed on right and left side (misalignment) also higher efforts were
noted
iii. In some vehicles (at dealer and
jerk from side (because striker get stuck in latch )
iv. Remark: Valid
3.2 Valid causes
Bonnet cable failure occurs
i. Bonnet as well as latch-striker alignment get
ii. During first locking-unlocking operation in alignment process, chances that striker get
stuck in latch.
Stack up analysis of top hood latch and bottom hood latch shows that only 2 mm
clearance given between the top and
not getting maintained due to contribution of hinges
On a vehicle which had run 7000 kilometers, front grill is removed; bonnet is
slammed few times and observed that bonnet is not
lever. Refer fig. 5 for explanation.
Fig. 4 Stack up analysis of top hood latch and
bottom hood latch
238
striker alignment getting disturbed over usage of vehicle:
Bonnet alignment observed, gap measurements done and bonnet efforts were taken on
customer vehicles during dealer visit
Gap variation is observed on right and left side (misalignment) also higher efforts were
In some vehicles (at dealer and production shop) bonnet got opened after giving slight
jerk from side (because striker get stuck in latch )
occurs because striker gets stuck into bottom latch.
striker alignment getting disturbed over usage of vehicle
unlocking operation in alignment process, chances that striker get
clearance given between the top and bottom hood latch for alignment as shown in fig
not getting maintained due to contribution of hinges and in process.
slammed few times and observed that bonnet is not opening by operating hood latch release
for explanation.
Stack up analysis of top hood latch and
bottom hood latch
(a)
(b)
Fig. 5 (a) Bonnet is not opened
striker got stuck into latch (b)
marks on bottom latch
hicle:
Bonnet alignment observed, gap measurements done and bonnet efforts were taken on
Gap variation is observed on right and left side (misalignment) also higher efforts were
) bonnet got opened after giving slight
ting disturbed over usage of vehicle.
unlocking operation in alignment process, chances that striker get
bottom hood latch for alignment as shown in fig. 4. It is
opening by operating hood latch release
(a) Bonnet is not opened because
striker got stuck into latch (b) Stuck up
latch

239
During dealer visit, customer vehicles were observed for bonnet alignment. Hood
latch release lever efforts were taken and bonnet gaps were measured. Table 3 shows effort
and gap measurement readings. Higher operational efforts were seen in customer vehicles.
Table 3: Effort and gap measurement readings on customer vehicles
Sr.
No.
Hood latch
lever effort
(N)
Gaps (mm)
RH Side LH Side
1 2 3 4 5 6 1 2 3 4 5 6
1 83.9 5 4.9 4.6 5.5 5.2 5.2 4.1 4 4.8 3 3.1 4.1
2 77.1 5.1 2.5 2.1 4.2 4.6 6 6.3 6.3 6.5 4.1 4.7 4.8
3 95.6 5 2.1 1 2.9 3.7 4.4 5.6 5.9 5 3.8 4 5.8
4 114.5 5.8 5 4.7 7.5 4.8 4.9 5.2 3.8 6 2.3 2.8 6
5 103 5 4.8 4.1 5 4.5 4.7 6.1 3.6 4.5 2.8 3.5 4.6
6 80.3 3.8 2.9 1.3 4.1 3.9 6 5.9 5.4 5.2 2.6 3.4 5
7 78.1 6.3 4.9 3.8 5.7 5.7 6.1 6.1 4.8 6.2 2.5 3.9 4
8 82.7 6 4.8 4.2 6.2 5.8 6 6 4.7 5.1 2.8 3 4.6
9 87.5 5.2 4.4 3.8 5.3 5.1 5.1 6 5.1 6.1 3.2 3.2 4.1
10 91.4 5.5 3.2 2.2 4.6 2.8 5.3 5.6 4.9 5.9 4 4.1 5.1
3.3 Why-Why analysis
Cause for bonnet cable failure is explained below,
i. Why: Higher operational efforts for hood latch release lever
ii. Why: Striker get stuck into bottom latch
iii. Why: Striker and bottom latch not remain inline
iv. Why: Latch-striker alignment getting disturbed over usage of vehicle or during first cycle
of alignment
v. Why: This factor is not considered during design
4. PROPOSED SOLUTION
As there is problem that striker of top hood latch assembly getting stuck into bottom
latch due to misalignment, there is a need of keeping striker and bottom latch in one line i.e.
to avoid misalignment (oblique travel of striker in latch).
After observation and study of structural design of hood latch parts of vehicle,
proposal is given to implement a groove in the striker of top hood latch and guide on bottom
hood to avoid misalignment and stuck up issue because of which bonnet cable failure occurs.
For this, structural benchmarking was done with hood latch of another vehicle as
shown in fig. 6 and 7.

(a)
Fig. 6 (a) Provision of groove in striker with proper cap to control the height after alignment
(b) No provision of groove and simple cap
(a) (
Fig. 7 (a) Provision of guide cup on bottom hood latch
According to proposal, design changes
vehicle. Following are the modifications in the design of hood latch bottom part, (Fig
i. Base plate center hole diameter is cha
ii. Flange is added in support plate
iii. Cable slot in cable holding bracket is changed
iv. Locking bracket (guide cup) is added
For hood latch top part, outer diameter of washer is reduced from 32 mm to 25 mm as
shown in fig. 9.
(a)
Fig. 8 Change in bottom hood latch
240
(b)
groove in striker with proper cap to control the height after alignment
(b) No provision of groove and simple cap
(a) (b)
Provision of guide cup on bottom hood latch (b) No provision of guide cup on
bottom hood latch
According to proposal, design changes were made in striker and bottom hood latch of
. Following are the modifications in the design of hood latch bottom part, (Fig
Base plate center hole diameter is changed
Flange is added in support plate
Cable slot in cable holding bracket is changed
Locking bracket (guide cup) is added
(a) (b)
Change in bottom hood latch (a) Existing (b) Proposed
groove in striker with proper cap to control the height after alignment
ovision of guide cup on
made in striker and bottom hood latch of
. Following are the modifications in the design of hood latch bottom part, (Fig. 8)

241
(a) (b)
Fig. 9 Change in top hood latch (a) Existing (b) Proposed
5. IMPLEMENTATION AND RESULTS
Sample hood latches were received from supplier with said design modifications in
given proposal.
5.1 Concept trial
Concept trial was conducted on three vehicles with new hood latch samples. Table 4
shows comparison of hood latch release lever operational efforts for three vehicles with
existing and modified hood latch parts.
Table 4: Hood latch release lever operational efforts during concept trial
Vehicle
No.
Specification
(N)
Readings with existing
hood latch (N)
Readings with modified
hood latch (N)
1 2 3 1 2 3
1 40-80 78.4 76.1 76.3 53.7 53.2 53.2
2 40-80 79.1 78.4 78 56 56.2 55.5
3 40-80 76.8 76.5 75.9 50.2 49.8 49.1
i. During concept trial, fitment was observed for any difficulties in fitment process as well
as alignment.
ii. No issue regarding fitment or alignment was noticed.
iii. After operating hood latch release lever and primary lock getting released, secondary lock
(to be released by operating lever of top side hood latch) was found ok in all three
vehicles.
iv. Bonnet opening-closing cycle was performed for 500 times on three vehicles with
modified hood latch parts to check whether there is bonnet cable failure. Bonnet cable
failure incidence was not observed and cable found ok.
5.2 Fitment trial
After receiving modified hood latch samples, fitment trial was conducted and
completed for five numbers of vehicles.

242
Table 5: Hood latch release lever operational efforts during fitment trial
Vehicle
No.
Specification
(N)
Readings with modified hood
latch (N)
1 2 3
1 40-80 56.5 56.2 55.9
2 40-80 59.3 58.4 58.6
3 40-80 50.2 50.2 50.1
4 40-80 53.8 53.5 53.1
5 40-80 60.4 60.9 60.7
No fitment related issue was observed during trial. Bonnet opening-closing cycle was
repeated for five vehicles and no abnormality was observed (No higher efforts, secondary
locking ok). Hood latch release lever operating efforts were measured on five vehicles and
found within specifications. Readings are shown in table 5.
5.3 Validation and part trial
Validation process is conducted for modified hood latch samples. In validation,
bonnet cable withstands and passed target of 5000 cycles of bonnet opening and closing for
all samples. Part trial is conducted on 200 vehicles and readings were taken. All vehicles
have shown effort readings within specification. No bonnet cable failure incidence was
occurred. Range of effort readings was found between 45 to 62 N (Specification is 40-80 N).
This shows significant operational effort reduction for hood latch release lever.
6. CONCLUSION
1. Root cause analysis is carried out for the concern “Higher operational efforts for hood latch
release lever which results in bonnet cable failure.”
i. Bonnet cable failure occurs due to disturbance in alignment of striker-latch which results
in stuck up condition of striker in latch.
ii. To avoid stuck up condition, design modifications are suggested in hood latch with
provision of locking bracket (guide cup).
2. Trials with modified hood latch samples showed reduction in hood latch release lever
operational effort than that in case of customer vehicles as well as new vehicles with existing
design.
3. In validation, bonnet cable withstand for 5000 cycles of bonnet opening and closing.
During trials as well as implementation for 200 vehicles, no bonnet cable failure incidence
occurred with modified hood latch.
7. REFERENCES
[1] R.d'Ippolito, M. Hack, S. Donders, L. Hermans, N. Tzannetakis, D. Vandepitte,
Improving the fatigue life of a vehicle knuckle with a reliability-based design
optimization approach, Journal of Statistical Planning and Inference, 139, 2009, pp.
1619-1632

243
[2] Alan S. Abrahamas, Jian Jiao, G. Alan Wang, Weiguo Fan, Vehicle defect discovery
from social media, Decision Support Systems, 2012, pp. 1-11.
[3] Senthilnathan Subbiah, O. P. Singh, Srikanth K. Mohan, Arockia P. Jeyaraj, Effect of
muffler mounting bracket designs on durability, Engineering Failure Analysis, 18,
2011, pp. 1094–1107.
[4] V. Veloso , H.S. Magalhaes , G.I. Bicalho , E.S. Palma , Failure investigation and
stress analysis of a longitudinal stringer of an automobile chassis, Engineering Failure
Analysis, 16, 2009, pp. 1696–1702.
[5] Roland Meuller-Fiedler, Volker Knoblauch, Reliability aspects of microsensors and
micromechatronic actuators for automotive applications, Microelectronics Reliability,
43, 2003, pp. 1085–1097.
[6] D. G. Yang, F. F. Wan, Z. Y. Shou, W. D. van Driel, H. Scholten, L. Goumans, R.
Faria, Effect of high temperature aging on reliability of automotive electronics,
Microelectronics Reliability, 51, 2011, pp. 1938–1942.
[7] ANOVA-C Guidelines in automotive industry.
[8] GD Guidelines in automotive industry.
[9] P.Vishnu, R.Ajaykrishna, Dr.S.Thirumalini, “Recent Advancements and Challenges
in Plug-In Diesel Hybrid Electric Vehicle Technology” International Journal of
Electrical Engineering & Technology (IJEET), Volume 3 Issue 1, 2012, pp. 316 - 325,
ISSN Print: 0976-6545, ISSN Online: 0976-6553
[10] Ilir Doçi and Musli Bajraktari, “Regulation of Vehicle‘S Left Turn in Urban
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International Journal of Advanced Research in Engineering & Technology (IJARET)
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0976-6499.

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