Mechanics

BATTERY DRAIN AND ERRATIC AC VENTS

2003 BMW 525i • 6 cylinder 2WD Automatic • 80,000 miles

On 2003 BMW 525i, with a 3month new battery, found car to be dead completely and alarm had gone off few hours before. Didn't know what caused alarm to go off, but was able to recharge the discharged battery to hold 1000 CCA (900 recd) at autozone. They found only 5.34 Volts left in new battery and said something is draining the car. Noticed a crookedly placed fuse for security alarm in the fuse box in the trunk near the battery (as I was looking for a drain) then put it in correctly. Put battery in and car was running again. Next day drove it around and noticed it was just not running smooth and noticed the cabin vents were blowing air irregularly and erratically with and without being turned on. This leads me to believe that this is the problem draining my battery. I do get a
'service engine soon light' but thought it may be from battery taken out, recharged and replaced. Car has never shut off on me on the road and AC vents have never done this before. Battery had died 3months ago after a bad thunderstorm overnight and thought that is what killed my battery previously. So my question is what is the problem draining my battery most likely? Is there an electrical drain pulling charge away from battery? Is it the vent problem or something else. What would be the typical repair in this scenario and can I save money and do it myself (in these tough economic times) or if I go to mechanic, how much would it run me approximately and what services should I expect. Thank you
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Jatnpatl
November 15, 2010.




First, I believe you have a couple different problems. The first thing that should be done is have the computer scanned. If the check engine light is on, it has a trouble code stored in the computer. Many nationally recognized parts stores will do it for free.

Next, the battery drain is a problem. What to do is follow the directions listed at this site under the "How To" section listed at the top of the page. If there is a draw, remove one fuse at a time until the draw stops and you then have isolated the problem circuit.

As far as the vents, they are actuated by engine vacuum. Most likely there is a vacuum leak under the dash. Check for that. If you are lucky, you may hear a hissing sound with the engine running.

Finally, (and I'll shut up), you have me wondering about the storm. I question if the vehicle was struck by lightening and blew out one of the diodes in the alternator. That would explaine the electrical draw with the key off. You may want to have the alternator tested at the parts store.

Let me know what you find.

Joe

Got the charging system tested at autozone and said the alternator, battery and starter are fine. Drove the car home fine, but next morning car would not start, lights dim in car as if battery dying again. No check engine light. What part of electrical would you check or what is next on the list?

Tiny
Jatnpatl
Nov 17, 2010.
The key off draw is the first item we are going to tackle here. The possibility the generic scan the auto parts store did was inconclusive is present. BMW has not been in the forefront of OBDII scanning technology and their proprietary equipment might need to be employed to uncover the root cause of the problems. There is also the possibility the final stage unit that controls the fan is compromised and will require replacement. This could very well be the cause of the drain you are experiencing. Realoem. Com is a site I like to use to get the part number(64116923204) and the retail price of the final stage unit. If you go to the site and put in the part number, it will pop up for you. The installation is quite straightforward. It is accessed from the passenger footwell area and the 1st thing to do is to pull the black plastic tray directly underneath the glovebox towards you as you sit in the seat, it will pop out. Then the carpet trim is held in by a single Phillips screw and some spring clips, take out the screw and push the carpet piece forward to dislodge the spring clips. There should be a wad of grey closed cell foam in the back corner, pull it out and you will be able to see the final stage unit, it has a 5 wire connector, push the plastic tab holding it in place and out it comes. Reverse the procedure for assembly and you are off to the races!
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Dr. Hagerty
Nov 20, 2010.

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