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Automotive/1998 BMW 540I Electrical Short

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Expert: - 5/22/2009


Question
When I turn the steering wheel on my 1998 BMW 540i to the right sharply the engine shuts off.  This happens both when the car is not moving and when moving.  If the car is not driven for a couple of days the battery loses its charge.  After turning the steering wheel to the right and the engine shuts of, the only way to start it again is with jumper cables, even though the battery is charged.  Any idea of where the short might be?  I suspect it is in the steering column but do not know how to access electrical wiring in the column.  Any ideas or suggestion? would be very much appreciated.

Answer
One presumes that the ignition lock is in the steering column, as it is in most cars in which the ignition lock assembly serves as a steering wheel lock as well.  From that perspective, I would say that you likely are on the right track as to the general location of the problems.  

I state this in plural because it is evident that there is more than one fault path involved - one which either opens or else shunts out the power to the ignition system when the steering column turns right, and another which provides an ongoing drain on your battery.  This latter one should be a concern, not only due to causing sulfation problems with the battery, but because there will be some resistance in this path which is heating up somewhere, and which may well arc open - scenarios which can result in a fire.

The matter of requiring jumper cables to restart, even with a good battery, is quite helpful - this suggests that one more of your problems probably is a failing battery clamp, either at its interface with the battery terminal itself, or between it and its stranded cable.  Clamping on the jumpers apparently bypasses this problem, or or re-establishes a partial contact.  All in all, there is evidence of a need to go through the system at large and deal with a few connection clean-up issues.  Many of these can be restored via cleaning and restoring the moisture-blocking and corrosion-preventive grease at clamps and connectors.

Beyond this, you want specific advice as to access and layout of the wiring systems in your BMW.  I don't have this, but you undoubtedly will get an answer or two from those who do.  Nonetheless, my pat answer to this always is to suggest that any person serious about carrying out repairs and - better yet - preventative maintenance on their own vehicles might just as well get the proper documentation and a few good tools and test instruments so as to do any job efficiently and  ... well, in style!

You have the right idea, and the will ... why not take it farther?

Cheers ... 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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