M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Electrical => Topic started by: fayjai on April 09, 2010, 09:10:46 PM
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As title says it, I just finish installing the hoses underneath my car and some reason when the car is off and keys out; the battery light on the dash remains on. Anybody have any clues?
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Possibly bad batteries on your SI board + corrosion. There should be a write up around here to check / replace them.
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I just had this problem hit me today. My "brake lining" light has been flickering for a month or so. Its very faint, so much that i cant see it in the daytime. I can only tell its barely on/flickering cuz its night. Then, tonight, my battery light came on after i turned the car off. It stayed on for about an hour when i got in it again to go home. It started right up and the light went away. No headlights dimmed or brightening with acceleration(not alternator).
I did a few searches and went to get a bite to eat so i could drive the car again. I got in, the light was still on after another hour, and started the car. Fired right up, only this time the light stayed on. I blipped the throttle and it started to go away. I blipped again and it went away. I got home and turned the car off. The light went off. I started it again to see if anything would happen. the car now keeps the light on while running, but goes out when the car is on?
why did it reverse? is this a sign of SI batteries?
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Check voltage at battery. You may have a junk battery, may be si board, may be alternator. Start eliminating things positively.
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checked the battery and alt out at autozone....
test done at 2000rpm, 53amps, 13.25V, and read bad diode
guess im gonna start looking......
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Problem is likely with a burnt diode in your alternator. If the ignition is off the diode will continue to draw power and your alternator light on the dashboard will illuminate. It basically turns on a circuit in your car thar should be off, and in the process draws power from your battery, will usually eventually result in a dead battery overnight. Could be something else, but this is the likely culprit... this isn't only with m42's, pretty much all vehicles could have this same issue.
Here's some info I copied and pasted from another site:
ALTERNATOR DIODE FAILURES
One of the most common causes of charging problems is the failure of one or more diodes in the alternator. Alternators have six diodes (three negative and three positive) that convert the alternating current (AC) to direct current (DC). They are called a diode trio because each negative diode is paired with a positive diode.
When the engine is running, charging current from the alternator flows through the diode trio via the BAT (B+) connection on the back of the alternator. A little current also flows through the charging light indicator circuit. On GM alternators, the indicator light circuit is terminal 1. On European alternators, the indicator light circuit is usually called 61 or D+. On Asian alternators, it is usually labeled L. This terminal leads to the ground side of the alternator warning light. When the alternator is charging, the diode trio supplies voltage to the ground side of the indicator light. This offsets the battery voltage applied to the positive side of the light, causing the light to go out once the engine starts. If the alternator stops charging, current flows though the light circuit from the positive side causing the charging system warning light to come on.
If one of the diodes fails, it may cause the charging system indicator light to glow dimly. If two or more diodes fail, the light will get brighter. At the same time, the feedback current from the diode trio will reduce the alternators ability to produce current. So the more diodes that fail, the less power the alternator will generate.
A bad connection or open circuit between the alternator output terminal and the positive battery terminal will force the charging current to follow a parallel route through the diode trio and out of the alternator. This heavier than normal current flow through the diodes will cause them to overheat and fail. Consequently, if you have replaced an alternator before because of bad diodes, and the replacement fails for the same reason, there is likely a bad connection or open circuit between the alternator BAT (B+) terminal and the positive side of the battery circuit. Do a voltage drop test to check the entire circuit.