eazye757

A couple months ago I was driving to work and during the commute the "trans fault", "tire pressure sensor" and "dynamic drive" malfunction lights came on and I felt a jerk. All this accompanied by the speedometer dropping to zero for a few seconds. I immediately pulled over and cut off the car and restarted it with no problems and drove to work.

Fast forward to last Friday, the same thing happened again( minus the jerk) but when I restarted the car, the lights remained. I cautiously drove to work with no decrease in drivability but lights on. Drove home fine that day but stopped at advance auto to have the electrical system checked and they told me the alt was fine but the batt was weak but still good. Got home and read up on it on this forum and everyone seems to be torn between replacing the battery and/or alternator for this issue. The light has come on every morning now (mon, tues) since but I started letting the car run before I leave for about 10 mins and then when i get in to leave, turn the car off and restart and have no problems on my morning commute.

I plan to replace the battery next weekend and ride with my girlfriend to work until then. I plan to go to advance for the battery over the Stealer. I will look into a indy to have the battery reprogrammed.

My question is since this is my first beamer, is there anything special I need to do when I change the battery? I have changed many batteries in my day and do most of my repair needs but fear some sensor being thrown and setting lost if i dont change the battery correctly. Also what type of battery is recommended for this car? Advance told me they dont change beamer batteries like they do other cars but they do provide a charger while I do the job.

Its a 2004 545 btw.

All input is appreciated!!

Thanks!!!

H F

On my car I delt with those same issues for weeks before the alternator showed any signs of goen bad. Since ur car is 9 yrs old I would put in a new alternator with the new battery . Also replace the charging relay in the trunk fuse box . Think about new belts pulleys and tensioners while ur replacing the alternator .

deansimpson

I've had the exact same issue lately.
My battery is only a year old so I'm wondering if the alternator is starting to go.
I got one of those cigarette lighter voltage checkers and before start up it is reading low, about
11.8 -12.0. After starting and while driving it's right where it should be, 13.8 - 14.2.
Alternator?? Oh, also my errors only come up right after starting the car.

eazye757

At first the lights waited a couple miles to come on but now like you, my lights come on about a min or so after start up. I'm wondering if the alternator is going bad now after reading H_F's post since by the time I had the alt system checked, the car had been running about 30 mins or so (from work to the store) and was at normal output. As suggested Ill just replace both to be on the safe side, the battery first and then the alt when I have a free weekend to devote to it. From what I've read sounds like its a PIA, removing the radiator and all.

Is there any specific type of battery I should get? I've seen people talk about AGM and others and I'm not to sure which way to go with that.

Also did you guys have your car reprogrammed after the new battery installation??

BimmerFan52

When replacing the battery do not rely on a list of replacement batteries at the auto store. You want to make sure the battery you buy matches the one coming out as closely as possible. A good starting point is to search this forum where specific battery model numbers are called out.

The size, location of venting port (some aftermarket batteries have multiple locations on the battery), type of battery (flooded lead acid which has a white top, or absorbent glass mat which has a black top), cold cranking amps, amp hour capacity should match exactly if possible. Take this information off the battery before you begin shopping and double check all of the specs before physically measuring the replacement battery and checking the vent location.

If you have an original FLA and want to change to an AGM type battery (generally considered a better more modern battery), then do not delay more than a day after installation to get the battery registered as the AGM will be charged by the DME at 14.8V maximum, whereas the FLA can be charged as high as 15.5V. The AGM will be damaged if a FLA type is coded and the DME signals the alternator to output a charge voltage greater than 14.8V for more than a few days.

When removing the battery be gentle with the cables and clamps. Remove the negative cable first, and insulate it with a rag before removing the positive cable. Both battery cables are very expensive and can easily be damaged with rough handling or prying with a screw driver. The negative cable has a small microprocessor integrated into it, and the positive cable has a small explosive charge integrated into it to remove power to the engine during an accident. Also, the bolt in the clamp is made of stainless steel and should not be excessively tightened, which can ruin the cable.

I just did my alternator about a year ago after exactly the same symptoms you are experiencing (I already had a cigarette lighter voltmeter and saw the alternator pump 17V one minute, drop to 11.5V the next and then settle in at 13.5V. Replacing the alternator is not that difficult but there are a lot of pieces to remove to be able to get the alternator out. OE Valeo units are available brand new under $300, which IMHO is the way to go, given the time investment. Rebuilt units can be good or bad depending upon the source and won't save you that much.

Also, think about the state of your coolant system at this time. If it is all original you should think VERY seriously about preventive maintenance of the coolant reservoir, water pump, thermostat, hoses, belts and vent tube. ALL of the things you will remove to replace the alternator must be removed to replace the water pump, except the harmonic balancer (crankshaft pulley). There will never be a better time. And while the failing alternator generally cannot do damage to the rest of the car (excepting very high voltage output due to a failing voltage regulator) a failed cooling system, especially if it happens at the wrong instant where you can't quickly exit the road and turn the engine off, can do very expensive damage to engine gaskets.

The rule about failure of the coolant system in a 545i is not IF but WHEN. The failures seem to bunch in the 65K to 75K miles range, but are not only dependent upon miles but to a great extent age (4-6 years old).

eazye757

I had been meaning to reply to you for quite some time and im finally doing it but you were correct on all horizons. I replaced the battery but the issues soon came back. It was the alternator as you alluded too. Not long before I changed the alternator out, my water pump started leaking as well. So as you recommended I did both jobs at once and changed out my belts as well. I still have to do the hoses but when I was in there, they still looked great.

Thanks for your input.

BimmerFan52

Glad it turned out well for you. These 545s are finicky, but a huge bang for the buck to drive. With their wide torque band they pull like a mule at any RPM. Pure fun.