Automotive/Headlight problem

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Expert: - 3/29/2011


Question
I have a 2006 Hyundai Sonata with V6 motor.  Last night I was driving and when using the high beam of my headlights they would dim and then brighten back up repeatedly.  This did not happen when headlights were on low regular beam.  Could it be the battery, alternator or the headlights?

Answer
I have no shop information on your Hyundai of course (for reasons given in my notes) but the problem is intriguing from the trouble-shooting perspective ...

This most likely indicates that an auto-reset circuit-breaker - one associated with or on the same bus as the headlight circuit - is cycling for some reason.  The fact that the lights will run bright and then dim, rather than run dim and then go out, would suggest that the bus feeding the high-beam circuit, and NOT the high-beam circuit itself, is being subjected to a short circuit to vehicle common.  When the short occurs, the voltage is pulled down, dimming your lights.  Then, when that CB opens, the voltage rises again, allowing your lights to return to normal brightness.

It is interesting that this occurs only for the high-beam circuit, and that the low-beam circuit appears to operate normally, thus nulling the possibility of a fault in the low-beam circuit as well.  However, I would wonder if there might be a fault in the headlight CHANGEOVER circuit, ie: within the dimmer switch or relay assembly.  It could be that this assembly happens to short the bus at the same time as it takes the low-beam lamps off the circuit when the high-beam lamps are selected.

You will want to isolate that changeover circuit, however it is configured, and check it out.

Happy hunting ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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