I was driving to church one Sunday evening in heavy traffic. When I came a few driveways before the church's parking lot, I activated my turn signal, applied the brakes, and turned into the parking lot. I was startled to hear a horn blow from the car behind me. It was odd that I hear any horn in my city, other than a general chorus of car alarms that go off on windy days.
When the service ended, I went out and put my foot on the brake. It was dark, so I would have been able to see the brake lights glowing. But there was a problem -- no lights. I got down on the floor and pushed the brake switch with my fingers. The tail lights lit up like a Christmas tree. But when I pushed the pedal, no lights.
I drove home (carefully) and disassembled the assembly. With my ohm meter I measured and found it working with minimal resistance. I grounded the brake wires and found the lights were working. I put it back together and again found that they did not light up.
It turns out that the switch was bad, but only when pushed at the right angle and with the right pressure all while mounted in the brake pedal frame. A $20 switch at the dealer solved the problem.
This entry was submitted by John Bate and edited by Jennifer Campbell.
John Bate has been a system engineer at Volvo Trucks since 1999, working with electrical harness design and process improvement. His background includes embedded computers and software, HF radio design, telematics, and writing copious amounts of simulation models and processes improvement software.
Tell us your experience in solving a knotty engineering problem. Send to Jennifer Campbell for Sherlock Ohms.
Publishing the explanations for those fault codes could be quite useful. I sold a car with the caveat "No guarrantee that it will get you home" because it would periodically die, often while running at 25 or 35MPH. No cough or sputter, just all at once no engine power. The new owner, a friend who purchased it understanding that it had a problem, eventually found that the "processor reset" code message was brought about by a very intermittent short circuit to ground of the power supply feed terminal, inside one of the fuel injectors. But how was that cryptic statement going to be traced to a short circuit leading to the reset?
3drob--publishing the technical specs and code for components will be a sure advantage to consumers. I don't think the average Joe will need them, while us DIYers will become more adaptable at working on these formerly "unfixable" problems.
That's reasonable and sound advice; but I think you are picturing something entirely different than the actual application I was troubleshooting. It wasn't mounting a motherboard on a chassis (i.e. like a computer tower or cabinet card rack); the situation was a mini transceiver with a diecast under casing, designed by the OEM for direct PCB mounting. The host PCB is intended to be handheld portable size, about 3 inches in length typically. So you might imagine why the detecting the failure mode was so elusive; because the design was in complete conformance with the developer's kit recommendations. (which now, is quite clear, illustrates its a potential failure mode waiting to happen).
Critic: You are correct and seldom do all the comments pertain directly to the original post. I learn things from some of the splinters and that makes these forums enjoyable. I guess my gripe was that when something fails it is not always a mistake. Sometimes things just wear out from repeated use and few of us would be willing to pay the price of a vehicle in which everything is built to last through eternity, even if that was possible.
As a closet libertarian it pains me to say, but yes Virginia, we need more legislation to protect the consumer. Car companies do the things they do to maximize profits for their shareholders and stakeholders (dealerships). Then they worry about the labor unions. Customers come last. In a cut-throat environment like the auto industry, there are NO new cars that I know of that are easily/cheaply servicable any more. Certainly such creatures (even if they did exist) wouldn't inspire a blog post here (an example of what you won't read here: "I changed my spark plugs last week, I could reach them all w/o lifting the engine or contorting my body, and it took 15 minutes", yawn.) I would interested to hear any examples of cars that are easy/cheap to service.
But, as an example of "good" legislation: look at the OBD ports in ALL modern cars. Such a thing would NEVER have existed without that legislation. In any case, legislation evens the playing field and allows/forces car companies to do the right thing without going bankrupt.
Mounting a PCB directly against a metal housing, with only solder mask as insulaiton is a bad, bad idea from a reliability perspective. All it takes is a pinhole or crack in the solder mask, and a little corrosion (or a little whisker/dendrite), and a short will develop. Thermal expansion/contraction could also eventually scuff through the solder mask. Space the board off the housing or use robust insulation.
More than one person has tried to mount a computer motherboard directly into a computer case with no standoffs. Guess what happens!
More legislation we do not need. Speak with your wallets! Don't buy cars you don't like because you can't easily service them yourself, or because parts are too expensive.
I agree. What's the big deal? Finding and replacing a bad brake-light switch doesn't require too much diagnostic effort.
On the other hand, it did get us all started writing these silly messages that we enjoy so much! Thanks, John.
One thing that puzzles me is why a Volvo engineer would write about replacing a bad switch. Certainly there must be something more interesting in his work that would be more interesting to readers as well, but maybe Volvo won't let him publish.
I was a comfirmed DIY for years. Points & plugs every 12,000 miles. Oil every 3 and filter every other change. Air filter at 12,000 when the plugs got changed, etc. We do not have to do that junk nearly as often any more. So the brake light switch went bad, big deal. Both mechanical and elecrical parts fail on occasion, and need replacing.
Autos are so much more dependable than years past that when something does go wrong it is worthy of a magazine article. It wasn't that terribly long ago that a vehicle with 75,000 miles on it was almost always ready for the salvage yard. I have fond memories of my first decent car, 1962 Buick with a 401 cubic inch engine,and AFB carb. I would love to have it back. But, I would not want it as my primary mode of transportation, because I am no longer willing to spend every other weekend working on a car. Or at least that is what it seemed like.
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