Study on Intermittent Failure Phenomenon of the Automotive

Environmental Light Sensor

Guangming Li

1, 2, a, *

, Wenhua Yuan

1, 2

, Jun Fu

1, 2

and Yi Ma

1, 2

Department of Mechanical and Energy Engineering, Shaoyang University, Shaoyang 422000, China

Key Laboratory of Hunan Province for Efficient Power System and Intelligent Manufacturing, Shaoyang University,

Shaoyang 422000,China

Keywords: Cars, Environmental light sensor, Intermittent, Failure, Tide, seal.

Abstract: According to the failure or intermittent failure of the FC-3AB ambient light sensor that feedback from the

production site of Geely Automobile, the vehicles in this condition were tested and it is found that after the

key hits the ignition lock ON file and switch the AUTO file, ark light environment (palm cover sun sensor)

lights automatically open function is failure. When the car headlight is turned on manually, the headlight

can be turned on, indicating that there is no problem with the car headlight. In this paper, the factors that

cause the failure are collated and analyzed, and the fish bone map is drawn. Through the analysis of the

quality of the ambient light sensor and the analysis of the process steps, it is determined that the solution is

to seal the sensor assembly to ensure that the internal circuit of the shell does not fail due to moisture, the

headlights of the car can be turned on normally, and the light in the car can be automatically adjusted.

Eventually, the correctness of the solution is verified through experiments, and the failure rate of the

automotive ambient light sensor is minimized, effectively improving the reliability of the ambient light

sensor and the safety of driving.

1 INTRODUCTION

With the rapid development of power electronics

technology, electrical control systems are

increasingly integrated (Wu gang, wang xiaoyu,

zhang Yang, liu jia, 2015) Among them, the safety

fault of automobile ambient light sensor is directly

related to the safety of driving and can not be

ignored. The failure or intermittent failure of the

ambient light sensor will prevent the car headlights

from turning on automatically, resulting in a greater

probability of accidents in traffic when a tunnel or

dark light section is encountered, which will

seriously affect the safety of the occupants. At the

same time, it also poses a threat to facilities outside

the car and pedestrians or other vehicles (Zhang

deqian, hong yuanquan, zhao yongquan, 2017)

And ... According to statistics, about 5,000 traffic

accidents are caused by driving fatigue during

driving each year, of which about 400 directly cause

death, and the situation in Europe is roughly the

same. In June 2017, there were 63 failures or

intermittent failures of the FC-3AB ambient light

sensors that were feedback from the production site

of the Xiangtan Geely Automobile Assembly

Workshop. The phenomenon was that the vehicle

was charged (the key hit the ignition lock ON file) +

after switching the AUTO file. Dark light

environment (Palm cover sun sensor) lights

automatically open function failure. In this paper,

the failure rate of vehicle ambient light sensor is

minimized and the reliability of ambient light sensor

is improved.

2 ANALYSIS ON THE CAUSES

OF FAILURE OF

ENVIRONMENTAL LIGHT

SENSOR

2.1 Environmental Light Sensor

Voltage Testing

After testing, the input level V2 of the normal part is

less than the output level V3 under dark light

condition, and the headlamp can be turned on

Li, G., Yuan, W., Fu, J. and Ma, Y.

Study on Intermittent Failure Phenomenon of the Automotive Environmental Light Sensor.

DOI: 10.5220/0008387400100014

In Proceedings of 5th International Conference on Vehicle, Mechanical and Electrical Engineering (ICVMEE 2019), pages 10-14

ISBN: 978-989-758-412-1

normally; under dark light condition, the input level

V2 is larger than the output level V3, and the

headlamp is not on. By testing the voltage of the

circuit, it can be determined that there is a quality

problem with the ambient light sensor assembly.

Voltage test values are shown in table 1 and table 2.

Table 1. Test results for normal parts.

Coding

Input

Voltage

V2(V)

Output

Voltage

V3(V)

Ispection

Results

373

125

qualified

396

142

qualified

367

119

qualified

402

183

qualified

421

166

qualified

385

152

qualified

397

169

qualified

372

143

qualified

Table 2. Test results for failure pieces.

Coding

Input

Voltage

V2(V)

Output

Voltage

V3(V)

Ispection

Results

298

672

unqualified

421

683

unqualified

361

1220

unqualified

200

872

unqualified

375

872

unqualified

321

962

unqualified

298

738

unqualified

342

697

unqualified

2.2 Photodiode Fault Troubleshooting

The photoelectric sensor fault screening, the most

important is whether the screening is photodiode

whether there is a quality problem, so the

photodiode also to carry out voltage testing. The test

of photodiode is also to verify the relationship

between input voltage and output voltage. As is

known to all, photodiode has one-way conductivity,

and if the photodiode is reversed, the resistance will

become infinite. The corresponding voltage will also

change, and this test is based on this principle to

verify whether the photodiode is qualified or not.

As shown in table 3 and table 4, the photocell

ratio of the two groups of components is basically

the same, and it can be seen from the voltage test

that they have one-way conductivity, which proves

that there is no fault of the two groups of

photodiodes, so the fault of the photodiode itself is

eliminated.

Table 3. Photodiode voltage test results for normal

components.

Coding

Input

Voltage

V2(V) (V)

Output

Voltage

V3(V)

Ispection

Results

19.26

qualified

19.14

qualified

19.24

qualified

19.07

qualified

19.33

qualified

19.12

qualified

19.27

qualified

19.36

qualified

Table 4. Photodiode voltage test results for fault

components.

Coding

Input Voltage

V2(V)(V)

Output

Voltage

V3(V)

Ispection

Results

19.27

unqualified

19.36

unqualified

19.14

unqualified

19.36

unqualified

19.33

unqualified

19.17

unqualified

19.07

unqualified

19.32

unqualified

Study on Intermittent Failure Phenomenon of the Automotive Environmental Light Sensor

2.3 Red Rubber Reflow Soldering Step

Checking

The so-called reflow soldering is to melt the solder

paste (solder paste) so that the surface-assembled

components and PCB boards are firmly bonded

together (Qi cheng, 2011). The equipment used is a

reflow soldering furnace located behind the mounter

in the production line. For example, table 5 is the

reference temperature of common red adhesive

reflow welding process, and the reference

temperature of three kinds of solder paste commonly

used in the table is at different temperature zones.

Table 6 is the equipment parameters of the

manufacturer. The solder paste used is SN63PB37.

You can see, the equipment parameters and

reference parameters are consistent basically,

because considering the time cost, this will be a

thing or two, three or four low temperature region

merging, and slightly increased the welding

temperature, but these smaller factor changes will

not affect the process to produce waste, therefore

rule out the possibility that this process has a

problem.

In addition, it is necessary to consider whether

the quality of the patch is affecting the overall effect

of the photoelectric sensor. So first check the patch

model, found no error. After the replacement of the

normal pieces of the patch, the products are OK.

Then check whether the patch position of the fault

parts is correct, and find that there is no part beyond

the welding pad at both ends, so there is no problem

with the patch. Therefore, there is no problem with

the process.

Table 5. Three solder paste reflow soldering temperature

Settings at 8 temperature zone.

Temperatur

e Range

SN63PB3

SN42BI5

SN96.CU

130°C

80°C

130°C

140°C

110°C

160°C

150°C

130°C

180°C

160°C

150°C

200°C

175°C

160°C

220°C

190°C

180°C

240°C

210°C

190°C

255°C

200°C

180°C

235°C

Table 6. Equipment parameters of manufacturers

1,2

3,4

140°C

170°C

190°C

200°C

220

190

2.4 Wave Crest Welding Procedure

Inspection

First consider whether the parameters for this

process are set correctly. First, consider preheating.

The tin furnace temperature of this process is kept at

250°C , which is consistent with the reference value.

Therefore, there is no problem with the process.

Then consider the transport speed (stripping speed).

Generally speaking, too fast stripping speed will

lead to PCB preheating not reaching the ideal

temperature, and too slow will lead to too high

temperature, which may damage PCB board.

Therefore, the speed is usually set at 1100mm-

1200mm, which is consistent with the

manufacturer's production parameters. Finally, the

quality of flux was considered. The flux model was

RF800, and the manufacturer was found to have the

production qualification, so there was no problem

with the model. However, it was observed that the

surface of the fault parts could help with flux

residue, and it was considered that poor contact of

the circuit was caused by flux residue. Therefore, the

surface of the fault parts was cleaned with washing

board water, and then assembled and tested. It was

found that the product could work normally, so we

considered that the intermittent failure of the

ambient light sensor was caused by the quality of

flux. In order to further confirm this idea, we applied

for trial production of 500 pieces of GOLF nh-4 flux

and put them into the refrigerator for moisture

regain. The final test results showed that no such

phenomenon occurred in all products. Therefore, it

can be concluded that the quality of flux causes

intermittent failure of ambient light sensor.

2.5 Wire Harness Welding Inspection

No broken skin or core leakage was found in the

wiring harness inspection. Therefore, the quality

problem of the two hardware is excluded. The

welding method is manual welding, and the

temperature is 350°C, which conforms to the

specified temperature.

Based on the above tests, it can be concluded that

the intermittent failure of ambient light sensor is

caused by short circuit due to poor flux quality. In

order to verify that the fundamental factor is the

quality of flux, make the following test again: clean

the flux residue of the failed parts with washing

board water, and then dry the test, and find that

100% of the failed parts can be used normally. Then

a control group was made again. Another part of the

defective parts were cleaned with plate washing

ICVMEE 2019 - 5th International Conference on Vehicle, Mechanical and Electrical Engineering

water and then dried naturally. Then they were put

into the refrigerator for moisture regain for two

hours. It is concluded that the flux residue absorbs a

certain amount of moisture and leads to short circuit.

3 IMPROVED DESIGN

As shown in Fig.1 (a), there is no gap in the buckle

part of the shell to prevent the water vapor from

entering, but the buckle cannot be recessed when

under pressure, so the sensor assembly cannot be

easily installed in the car. If a large pressure

assembly is used, it may crack the sensor housing

and cause water vapor to enter. It is planned to set an

impervious groove in the location of the buckle.

Before drawing the groove, the dimensions of the

buckle and the shell should be analyzed. In the

modeling process of the original part mentioned

above, the shell thickness is defined as 1.05mm, and

the buckle height is 3.6mm. Suppose the groove

depth is defined as 1.0mm, the sensor assembly

moves the distance of the buckle to the inside when

assembling, which is 1.0mm, making it difficult to

assemble. Therefore, to increase the depth of the

groove, the inner wall of the shell should be

thickened. The improved design is shown in Fig.1 (b)

and Fig.1 (c).

(a) Fault component model, (b) The design of the grooves,

Figure 1. Comparison of models before and after

improvement.

Because the size of the base is designed

according to the outline of the bottom of the shell,

there will not be too large gaps in the assembly.

Sealing performance, in order to guarantee the

assembly requirements shell and base are assembled

on the base of the surface coated with sealant, if

adopts the integration of welding seal due to the

welding quality is not controllable, can cause there is

not roa (Zhang cao, 2008), and the price of this

product is very low ambient light sensor, when the

sensor in the cause of the problem, only need to

replace the sensor, so apply sealant is appropriate.

4 IMPROVE THE

EXPERIMENTAL

VERIFICATION OF THE

DESIGN SCHEME

Considering the contingency of failure, 300 pieces

of environmental light sensor with improved design

were trial-produced, and the test results were 100%

qualified rate, and the voltage was V2 less than V3.

Therefore, the possibility of deviation of

experimental results caused by product quality

problems is excluded.

Although the sealing technology is not a leading

technology, it is often a decisive key technology

(Chen feng, zhang wei, wang xunming, 2011). The

sealing technology in this paper is related to the

safety and reliability of vehicles, so it is necessary to

conduct an extreme environment test for the

inspection link. Check the sealing performance of

the product, put the product in the refrigerator for

moisture regain, so as to expose the product to the

air with the relative humidity of 100%, and simulate

the air environment with extreme humidity as much

as possible. In order to verify that the product can be

used reliably in a humid environment for a long

time, the moisture return time is specially set as 3

days. After the return of moisture, the voltage of the

ambient light sensor was tested, and it was found

that 100% of the input voltage of the product was

lower than the output voltage, and the voltage was

normal. The product is then assembled into the

vehicle, and the headlights can be started and opened

in the case of dark light. Cover the sensor with your

palm, and the headlights can be automatically

opened without failure.

Study on Intermittent Failure Phenomenon of the Automotive Environmental Light Sensor

5 CONCLUSION

Based on the ambient light sensor failure

phenomenon appears in the car caused headlight,

opening and closing failure first detect the quality of

optical sensor, found the photodiode itself there is no

quality problem, second to the ambient light sensor

process troubleshooting steps, mainly check the

reflow, wave soldering process, and found in wave

soldering, flux residues led to the sensor failure, the

last light sensor wiring harness for testing, test is

normal, thus determine only flux residues led to the

failure in the product. The failure reason is that the

flux is affected by moisture and water absorption,

resulting in short circuit of the circuit board.

According to the failure reason, the improvement

plan is to seal the shell, mainly to improve the size

and position of the shell and base buckle. Define

grooves to ensure that the buckle can move inward

under pressure and ensure the sealing of the shell; In

order to ensure no gap between the base and the

shell, interference fit is adopted. The rationality of

the improved design is verified by the sealing and

reliability test of the new product.

ACKNOWLEDGMENTS

Fund projects: outstanding youth project of

education department of hunan province (16B235),

general scientific research project of education

department of hunan province (17C1444 and

16C1432), and CX2016SY015 of postgraduate

scientific research innovation project of shaoyang

university.

About the author: li guangming (1983-), male,

born in shaoyang, hunan province, master degree,

mainly engaged in vehicle engineering teaching and

research of automobile testing technology.

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ICVMEE 2019 - 5th International Conference on Vehicle, Mechanical and Electrical Engineering