I owned a 2009 Audi A3 with a rear lightbulb error that eventually led to a lightbulb failure. For months there was a nagging error icon on the instrument panel that indicated one of the rear brake lightbulbs was out. When I finally checked, I found that all the brake lights on the rear of the car were working, even though the indicator displayed a problem. On a subsequent check, I found that two of the bulbs had burned out.
With the annual safety inspection looming, and half the brake lights not working, I finally had the incentive to fix the problem.
When I removed the rear light assemblies, I discovered that the non-functional lightbulbs were still good. The bulb holder assembly is a three-dimensional injection molded plastic unit that combines with a three-dimensional formed galvanized steel sheet metal frame that serves both as a structural holder and electrical conductor. The sheet metal frame is swaged to the plastic structure by thermally melting six studs.
Two years in the Texas heat had raised the temperature of the plastic to a level that the creep strength of the plastic was exceeded. The two bulbs that didn't light were in an assembly where the plastic actually flowed between the sheet metal holder and the ground cylinder of the lightbulb. The steel frame had raised about a quarter inch off its intentional mounting and tilted, allowing the ground frame to contact plastic and initiate the plastic melting. That broke the circuit.
The dealer was out of stock on this assembly, which was just as well. The price of each assembly was about $100 with tax. So I decided to break the studs off, then drill pilot holes for #4 sheet metal screws to replace the swage studs. All the lights now work perfectly, and the instrument status error has been eliminated.
While I admire the simplicity of the design, its execution failed under conditions that should have been within the designer's requirements. It isn't clear whether the sub-tier supplier cheated by using the wrong plastic, or if this is a common design flaw, which has gone unresolved over the five-year production run of this model.
This entry was submitted by Kirk Miller and edited by Rob Spiegel.
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My friend is a Jaguar fan. A few years ago he finally got to buy a Jaguar. He was telling me he had to replace a part of the dashboard. His theory was that Jaguar designed the car according to the weather in England = very few hot and sunny days. So, in a climate of many hot and sunny days, the dash didn't survive. Perhaps the Audi problem is a similar climate difference effect.
I used to own a Saturn LS series sedan. It had the same injection molded light assemblies. It had the same failure (many stops by police for taillights out ensued). I went to the junk yard to get new assemblies as mine became pitted from the poor contact. I found a car with another harness attached to the light assembly that converted back to the more traditional plug in method of connecting lights. It seems there was a quiet recall on this. Maybe Audi has the same thing going on.
Considering all the checks and balances in automotive production and the amount of testing required when new materials are introduced, I'm always surprised to hear that something like this gets through. Texas can be very hot, but it sounds like the model didn't account for those heat extremes. Or it was a model built for one region, as Glenn's comment suggests, but sold in another region. Some Made by Monkeys columns, like this one, should perhaps be titled "Fixed by Clever Humans."
Clever may not be the best description, curious is. Being a design engineer by trade, a faulty design is like a challenge to a duel. To win the duel, the design modification needs to have superior durability while not taking excessive time, money or effort to implement. Realistically, these faulty designs are an excellent opportunity to baseline various approaches, observing practices that work well and others which don't.
Wait a minute; if any car company designes its products for a mild climate only, it would almost be called a fraud! I would say that it is a case of SLOPPY design, more that anything. In order to withstand the required mechanical stress in this type of assemblies, both the plastic part and the metal one have to be designed and fabricated properly. Asembly fixtures also play a part, as the melting tool too. Most commonly, the metal part is badly manufactured, since the punching leaves small, sharp edges that easily cut and erode the plastic bosses that are already stressed by the assembly heating-cooling cycle, which causes modified properties, different from the rest of the molded plastic part, then the bosses break easier than desired.
Your solution (to use small metal screws for plastic assemblies is the best way to ensure a proper, well joined assembly, well sealed from rain and spray. I woul write to the car maker; otherwise cars will be made even more sloppily every year.
Well, Jaguar is an expensive brand that has many issues... I would suppose that a Typical owner would want to keep a Jaguar car for several years; so that a badly damaged dashboard is inexcussable! Poor, insuficient design and testing by Monkeys-R-Us.
Amclaussen; I have read articles about how U.S. car manufacturers will do cold weather testing in the Dakotas, where very cold winter weather is readily available. And very hot summer weather is available in the southwest states. I don't think the U.K. has such weather extremes readily available. (Are there U.K. climate experts reading to comment ?) So it may not be a matter of designing for a mild climate, so much as the climate where the teating is done is mild, so the failures due to extreme climate are not seen during testing. Does anyone know if Jaguar or Audi have climate chambers to similate extreme climates ?
That's a very good question, GlennA. I would guess it depends somewhat on the size of the foreign market. Does the size of the market warrant testing outside the expectations of the core market? If the U.S. market is 2 or 3 percent, they may not see it as economically feasible to test for the market or design for the market.
I like you suggestion for the name of this blog, Ann. "Fixed by clever humans" is what this is really all about. I, too, am surprised that something like this happened. I'm not sure, but I believe that most of these automotive parts are designed for temperatures ranging from minus 30C to +70C (could a reader with expertise please weigh in here?), which would mean that it would be designed for about 160F on the upper end. Seems like this shouldn't have happened, even in the Texas heat.
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