BimmerFan52

Likely the alternator voltage regulator, but ???

Critical Data ? 2004 545i, 85K miles, battery is 5 months old (BMW dealer installed and registered), original alternator (not sure if Bosch or Valeo). Surpentine belt is adjusted properly and all connections (including ground) at battery and under hood have been checked and are solid. IBS has been tested and is operating properly. No electrical problems of any kind experienced until four days ago.

The last four days when I start the car cold (with all accessories off) the alternator outputs a very high voltage (over 17V measured under hood and directly on the battery terminals with a good voltmeter for 30-40 seconds) and then dies back down to 13.2-13.8V. Of course the whole electrical system freaks out and the dash lights up like it is Christmas with transmission, active steering, active roll stabilization and DSC error lights and no iDrive, no radio, no blower fan and no windows (lots of fun in Phoenix while it has been 115F).

If I drive a mile (with systems disabled) and then turn the engine off, pull the key and then start it again (may take several attempts) all of the faults go away except ?service engine soon? indicator light. The voltage then fluctuates between 11.4 and 13.9 as I am driving (measured by a little cigarette lighter voltmeter which I know reads about 0.3V too low). Eventually even the service engine soon light goes out. The car drives great, with full power, all accessories and no dimming or brightening of lights when engine RPM changes. The engine can be stopped and started while warm and drives perfectly with no faults.

After turning the engine off the battery measures 12.68V (as it should for a fully charged new battery). The next day the battery still measures 12.68V with engine off so I know there is no parasitic draining. However, upon starting the engine cold the voltage again goes over 17V, warning lights are shown and systems are disabled.

I am almost positive it is the voltage regulator in the alternator. I am happy that the alternator has made it to 85K miles and will be swapping it out with a new Valeo unit soon in any case (and I will probably replace the water pump and thermostat as they are original and I will already have the fan shroud and fan out of the engine bay ? plus I won?t have to worry about dripping antifreeze on a new alternator later).

MY QUESTION: Has anyone experienced SPECIFICALLY too high a voltage output from the alternator that was later discovered to have been caused by another component such as an electronic module, make contact relay or any other issue?

It is critical that I address the high voltage, which can damage electronic modules, the IBS and easily cook the battery. But I don?t want to put a new alternator in and then expose it to the stress of high output if something else is causing the alternator to push a high voltage.

Any thoughts? (Thanks in advance).

sanjsanj

STOP DRIVING IT!
It's your voltage regulator.

Someone else has had this problem too, 17v just like you, and he ending up frying his whole iDrive system, and that cost him a couple a g's.

The voltage then fluctuates between 11.4 and 13.9

This, again tells me your voltage regulator is effed. It should stay in the 13's, only momentarily dropping when letting go of the gas (certainly on a diesel)

My voltage regulator went too, but ended up intermittently making no juice instead.

It's a valeo alternator. Try and source the voltage regulator, it's hard to source it in the UK the one shop that does do it said it was £120. The whole alternator from a breakers yard was 80 so it was better going down that route in case the bearings or brushes decided to conk out too.

BimmerFan52

Thanks for the heads up on potential damage to the iDrive system. I will stop driving it.

I just had the electrical system tested at auto parts supply store and their computerized tester confirmed the alternator voltage regulator is bad.

I considered replacing just the voltage regulator or swapping the whole unit with a rebuilt one. But the existing unit has 85K miles on the bearings and the price difference between a rebuilt unit and a brand new one is only $100 (brand new Valeo OE unit is US$283 delivered) so it is not worth messing with a rebuilt unit. I'll also replace the original water pump and thermostat while I have everything apart as they are probably reaching end-of-life.

Thanks again!
Cheers

sanjsanj

WOW, a brand new alternator from the stealers here is £700! That's $1100

545felix

where are you sourcing a brand new Valeo for $283 shipped? I thought I had gotten mine cheap at $309 delivered. Since my car is currently on its THIRD alternator I'd like to keep a close eye on the lowest price for a replacement.

BimmerFan52

WOW your third alternator? My wife was giving me the business last night for buying a BMW and having to replace the original alternator at 85K miles! She reminded me that of all of the Toyotas, Hondas, Nissans, Mazdas and Lexuses we have owned, all driven from new to over 100K miles (some 150K), none ever needed an alternator replaced. I agreed, but told her that none of those cars ever caused the $hit eaten grin on my face that driving my 545 does.

I normally place parts orders on-line, but seeing the $283.50 price shown I called to confirm it was brand new and came with the pulley installed. The customer service rep confirmed the info and then said it would be $315 (the regular price shown). I told him a sale price was shown on the Web and he said they don't always have visibility to all the sales prices from their terminals and he would round it down to $283 even. Then he said unless I needed anything else he would get off the phone and make sure the order got to the shipping department in the next 10 minutes (it was 6:50PM CST where he was in TX) so it could ship that night. This morning I confirmed it did ship last night. Great service! http://www.carpartswarehouse.com/car...lternator.html

Amazon was $301 delivered
I considered a rebuilt but it is such a PITA to pull it out that I wasn't going to skimp. However, this outfit did impress me with a two year warranty on a rebuilt unit. They also sell component parts if you have the patience and skill to rebuild your own unit. Their website also claims that sometimes rebuilt units aren't in stock and they will substitute a new unit at the same price!
http://www.maniacelectricmotors.com/180ampvaatfo.html

I'll be replacing the water pump, thermostat and both belts while I'm in there, as they are all original also.

BimmerFan52

Yeah, the US market is so huge and so competitive that the large parts distributors here beat each other's brains in - and the consumer enjoys great prices!

I bought all new: alternator, water pump, thermostat, water return pipe, gasket, serpentine belt, AC compressor belt and 2 gallons of BMW coolant for under US$500.

545felix

in all fairness, with all the BMWs we've owned, the 545 is the first one I've had to touch the alternator on. Up until this car I thought BMW used bulletproof alternators. (of course, all the others had Bosch alternators, but don't get me started.)

BimmerFan52

I didn't know anything about Valeo before I started my search. Turns out they are a pretty large French manufacturer.
I looked for Bosch first but got no hits when I searched. It is possible I just didn't search long enough. It would be strange for BMW to single source such a major component.

In your cases, was the failure mode always the voltage regulator, or did the bearings or main windings fail in some?

Any theory on why the 545i alternators don't last?
1. Too much heat?
2. Defective design of car charging system putting extra stress on it?
3. Poor alternator/voltage regulator design?

Also wonder what experiences the 7-series crowd had with the same alternator?

I haven't looked at other manufacturer's alternator designs in detail, but if a common failure mode is the voltage regulator, it would be nice to see a design where the voltage regulator could slide out from the top of the alternator without having to remove the alternator from the car.

sanjsanj

This is possible to do as it sit's right at the top of the alternator. Clearance is the only issue, and on the 6cyl diesel's there is enough room. never looked under the bonnet of a petrol e60 so can't comment.

pictures:http://imgur.com/a/ch1Fz#0