electrical on 1998 BMW 318i

lately when am driving along and step on the brake pedal,my radio goes off and comes back on,the instrument lights flicker and sometimes the clock/temp display resets. sometimes this also happens when i use the turn signal. sometimes the ABS and auto traction control lights come on when i brake or engage cruise control. today i was doing 70 on the highway and turned on my lights and the car hesitated for a second and all the instrument warning lights came on and went off immediately. sometimes when am parked with the car running and i step on the brake pedal,the instrument and headlights flicker and radio goes off and comes back on. if i turn the key to kill the motor,radio and all instrument lights go off and come back on. this problem occurs intermittently sometimes going away for a week. help.

by in Overland Park, KS on November 12, 2009
1 answer
ANSWER by on November 13, 2009
This type of problems are a nightmare. First confirm battery voltage particularly if you can get to the battery when the car is malfunctioning. At rest the battery must have 12.6 volts engine running at idle the battery voltage across the battery should be approx. 14.6 volts, Bosch alternators sometimes are lazy and the battery light may glow until engine RPM is raised (its a sign of a failing/failed alternator). Once you have confirmed battery voltage is OK and alternator charging is probably OK (these simple voltmeter tests are by no means substitute comprehensive battery load test alternator diode and phase tests), check the battery connections are clean and tight and check battery ground, engine ground and then start plugging in and unplugging as many electrical connections as you can inspecting for corrosion build up on any connection. You can use di-electric grease or electrical contact cleaner available at Radio Shack and use this on any connector you have opened/disassembled. Look carefully at all your fuses, sometimes a fuse only partially blows. Tracing an intermittent problem can be frustrating but it sounds like this is getting to the point where the car may be dangerous to drive. It sounds like a power or ground issue. There is a You tube video about checking for "voltage drop" which is good and may really be relative to the trouble shooting you will need to do. A good digital volt meter and wiring diagram will also be needed, look at autozone website they have some popular vehicle workshop manuals on line for free.
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