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Sherlock Ohms

Strange Connections Killed the Mercedes-Benz

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patb2009
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Platinum
over-engineering
patb2009   11/1/2015 1:29:53 AM
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the safety systems and the engine systems should be on independent fuses.

 

 

JABova
User Rank
Iron
Re: over-engineering
JABova   11/2/2015 10:07:02 AM
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But separate fuses cost too much :-)

bob from maine
User Rank
Platinum
Complex cars
bob from maine   11/2/2015 10:25:19 AM
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MB makes some extraordinarily complex cars and in my experience, they are more than helpful in troubleshooting electrical issues, providing copies of schematics, Recall notices, TSBs to any who ask. Tying a passenger occupancy sensor to the engine idle solenoid - along with probably a bunch of other stuff, makes troubleshooting really tough. I've spent more than my share of time proving that the observed problem can't possibly exist based upon some aftermarket shop manual. I'd say finding an intermittent problem in the seat sensor was a real stroke of luck. That would have been a good day to buy a lottery ticket I think.

 

Larry M
User Rank
Platinum
Two similar instances
Larry M   11/2/2015 4:03:20 PM
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It reminds me of two similar instances. The MB wasn't the only car Made by Monkeys.

 

1) The taillight fuse on our 1976 Datsun B-210 would blow every couple of years. It wasn't frequent enough to chase down. But one day I was cleaning the car and lifted the carpet for the front passenger seat. Underneath was a four-wire flat cable. As I lifted it from the floor pan to vacuum under it, it stuck, then came away. There was a tiny, sharp metal burr which had penetrated the insulation. It wasn't long enough to contact the wire strands--except when a passenger planted a heel right on top of the cable coincident with the driver pressing the brake. I filed the burr off and never blew another fuse. Just serendipitous that I found it--and recognized what I found. I probably never would have found it if actively looking for it.

2) There doesn't seem to be any strategy as to what options are on what fuse circuits. I was trying to diagnose some problem on my GF's 2006 GMC Yukon XL and I couldn't get any response at all on the OBD II port. I had fearful visions of dollar signs as I imagined a failed Engine Control Module. Fortunately these things are now widely discussed on internet forums. After a quick search I asked her "Has one of the cigarette lighter sockets on the console stopped working?" She replied, "Yes, I loaned the car to my son-in-law a few years ago and it hasn't worked since." There doesn't seem to be a good reason why these two functions are fused together (except, of course, that neither is an immediately essential function). BUT it sure would have been nice had GM documented that. The owner's book just describes that fuse as cigarette lighter, doesn't mention the OBD II function.

patb2009
User Rank
Platinum
poor understanding of value
patb2009   11/2/2015 7:38:34 PM
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I don't mind having 3-4 fuse boxes in a car... In fact it eases troubleshooting,

but I really hate tying things together.

 

it's very poor value engineering.

 

 

William K.
User Rank
Platinum
Re: over-engineering
William K.   11/2/2015 8:45:10 PM
What should be is that designers should be forced to consider the secondary results of their actions.  More likely to happen, the companies should be forced to list every item fed by each fuse. When I say "forced", I mean not allowed to sell the products, no matter what, without the required information. That kind of force would get cooperation. AND the information to produce such a list already exists in their design files, so it should be easy.

patb2009
User Rank
Platinum
Re: over-engineering
patb2009   11/2/2015 9:22:53 PM
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thats a govt regulation and most people here hate regulations

kasone
User Rank
Iron
Re: over-engineering
kasone   11/3/2015 7:33:47 AM
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Not necessarily, if the leaders at the top instill a culture of excellence in the products, no governnment regulations are needed.

Larry M
User Rank
Platinum
Re: poor understanding of value
Larry M   11/3/2015 9:13:44 AM
NO RATINGS
Patb2009 wrote "I don't mind having 3-4 fuse boxes in a car... In fact it eases troubleshooting."

Umm, yeah, the Yukon XL does have multiple fuse "boxes." That didn't stop GM from putting the OBD II port and cigarette lighter on the same fuse.

John_Reed
User Rank
Gold
shorts and opens
John_Reed   11/3/2015 10:46:48 AM
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Given accurate diagrams, or even better, computerized wire listings, opens are easy to find as long as you can get physical access to conductors. Shorts are another matter, and intermittant shorts can consume inordinate amounts of time and expense.

At my plant we had two contractors simultaneously installing two major upgrades in the same bay of a building. Both teams had hand drawn wire lists and both started numbering their wires sequentially with wire #1. Many of the wiring junctions were in boxes that were very hard to access. There were no terminal strips in many of the junction boxes and we ended up with many cases where the two systems had totally unrelated conductors tied together labeled with identical wire numbers.

 It was a perfect storm of confusion. When checkout began, some components immediately went up in smoke. Wire #1 of system A was connected to wire #1 of system B. When this was corrected we got all the way to wire #3 before dealing with the next error.  It took months to correct all the errors. All this waste of time and effort would have been avoided had management simply specified to the contractors a numbering system to use in identifying cables and conductors.

There is no excuse for failing to document every conductor in a newly constructed facility in a data base, which can be sorted to show all the terminal points connected to any electrical circuit node or all the electrical nodes on each terminal strip or subassembly connector.

 

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