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I see a lot of topics: "please help!", "why it does not work?", etc. As a mechanical engineer, I've been following some basic methods to solve issues. As obvious as it could seem for some, it seems everyone is not following the same path. What about we try to gather methods to solve problem by ourself? I believe everyone should do his homework first prior to request some help. Most of the time, first answers from members are other questions. What about we try to provide some answers to questions instead? Of course, the first move should be to search for already known issues. there's tons of lessons learned to be shared on this board. OEM's are using some problem solving form such as 8D at GM. it helps to: - Define the issue - Prevent it (in the industry, it usually mean "check parts & scrap bad ones" ) - Find the root cause - Find a corrective action - Make sure it solved for good 2 very basic tools, one is a method "5-why", the second tool is to move forward in the process: fishbone diagram. 5-why. This is what I'm using when I have a problem: I ask myself why, why, why until I've got a root cause to solve. Usually at the 5th "why", we've got the answer. The goal is not only to solve the issue but also to prevent it to happen again. That's very basic quality process. Example: Issue: My headlights do not work. 1st why: Why don't they work? -> Bulbs are broken? - no -> Fuses have melted? - Yes -> Harness is damaged? - No, checked with ohmmeter -> Connectors are bad/corroded? - No, they look ok -> Headlight switch damaged? - No, it was in good shape -> etc. - because there's probably 10 more items to be added if we'd like. 2nd why: Why did my fuses melt? -> Fuses are too weak? - No, they were 15A (instead of 10A) -> Fuses holder is corroded? - No -> Corrosion in connectors? - No, I've checked earlier -> corrosion in headlight housing? - No + when I disconnect them, fuses no longer blow (hint!) -> I've got a wire grounded somewhere? - No, every ground is showing continuity with chassis & Engine -> I've got a short somewhere ? - I notice position light bulb (inside headlight housing in my case) is having 10V instead of ground & 12V from regular signal wire. 3rd why: Why do I have 10V & 12V at position light bulb? and why position light issue would interfere with headlights? -> Wire is damaged somewhere ? - No, everything is good as stated above. -> Because I've hacked my headlight harness to pass European regulation with +12V signal taken from side markers? Human related error? how could that be? -> Because I've hacked my headlight harness to bring a ground to position light bulb? I've got +10V instead of ground! I've added a wire going from a black wire labeled "ground" to position light bulb. 4th why: Why "ground" black wire is providing +10V instead of being ground? -> Nissan/Datsun did a mistake? -> Previous owner has hacked also the harness thus changing everything? - Obviously yes since no wire has the correct color coding when referring to service manual. -> Because I haven't checked proper tension before setting everything up? No need for 5th why here ! The causes of the issue: -> Harness has been modified -> I did not check everything while doing the work - Lesson learned! (hopefully!) -> Wires are improperly crimped together, I had to changed the way they were setup. I've controlled everything with a voltmeter during the process! Problem is solved & I'm positive it won't come back. Fishbone diagram or cause-and-effect diagram This one helps to get proposal for every "why". It starts with a consequence: "fuses have melted" for instance We should split then items into categories. the book is saying to split them into 5 major ones: People, Methods, Machines, Materials, Measurements, Environment. I don't usually follow exactly those steps. The point is to think about anything that could be the cause, it is a brainstorming step. This is where forum community could help the most. Image from Wiki: In materials, we would have broken wires & harnesses, corrosion issues, too weak fuses, etc. In Environment, we could also have corrosion, debris somewhere, salt in connectors In people, we could have fuses improperly clamped, etc. Management category here is useless With such process, we've got tons of stuff to do to make sure we don't miss anything. If everything is done right, nothing would be missed! This is how I've fixed headlights issue that was there for 3 years in my car in 2 days. I was just driving the car during summer time with day light to go around the issue Since it was pulling power from the system, my car was also stalling at red lights sometimes...call me stupid! These are also the basic tools that avoided my company to recall 300,000 cars because of issues....
