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Cruise Control

Posted by alanrw 
December 31, 2009 09:51PM
So the cruise control on my 325E goes out. Remembering the right brake lamp bulb trick, I open the trunk, pull the passenger side light assembly. The brake lamp bulb and socket look darn good but I go ahead and pull out the 400 grit sand paper and polish the bulb and socket. Sure enough, the cruise control is back.

What is the deal with that, the brake lamps were working fine but I guess a minute amount of resistance tanks the cruise control?

alan
December 31, 2009 10:12PM
Quote
alanrw
So the cruise control on my 325E goes out. Remembering the right brake lamp bulb trick, I open the trunk, pull the passenger side light assembly. The brake lamp bulb and socket look darn good but I go ahead and pull out the 400 grit sand paper and polish the bulb and socket. Sure enough, the cruise control is back.

What is the deal with that, the brake lamps were working fine but I guess a minute amount of resistance tanks the cruise control?

alan

Hi Alan,

Along with the brake light warning on the 'check' panel; this is a slight short coming in electrical engineering on the part of the BMW designers.
They overbuilt the mechanical components like engines by 50% but relied on third party companies for the electrics(Siemens etal). With the info at hand they designed the electrical systems with the usual 50% margin...but the suppliers were, apparently, working to a slightly different tolerance sad smiley

Simple things like relay contact points being burned and becoming resistive over time were not or could not be included in the original design calculations.

Somewhere in the system, there are sensors that are designed with too tight a tolerance.
Fortunately, we only have to live with the inconvenience, rather than real failed components...most of the time grinning smiley
January 05, 2010 11:32AM
Update: about 2 years ago, I replaced my dash pad. After I got everything back together, I noticed that the Range function on my onboard computer was off after reassembly but everything else worked. Ever since cleaning the contact on the brake light, the Range function is back to spec!!!

I guess I will have to make a note every Jan 1., polish the contacts on the brake light bulb and mount!!

alan
January 05, 2010 05:23PM
oh goodness! i'm going to try this with my 190E...

'93 190E 2.6 » days
'92 318ic » weekends
'85 280TE » resto
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