battery/alternator warning light

[mitch1981]

CDI 220 2003 hi, jus wondered if anyone has any ideas what is causing my battery/alternator red warning light to flash on, if i drive for quite a few miles it just about on all the time, the battery is only 1 year old and isn't beind drained as on a night the lights radio and heaters can be on, but my car isn't stood for a number of days so i dont know if it will be dead if left for a few days, will the alternator need changing, if so is this a big job, thanks

 

[nippynoo]

I've got a similar problem . Battery/Alternator message (2006 C220CDI). Took it to a Kwik-Fit and they said faulty battery. Of course they would, as they had one ready to fit, but I dont think it is, so I didnt get one. Many people replace batteries only to have the same problem 2 days later. So its more likely to be one of the following:

(1) Alternator (these are water cooled, so lots £££, unreliable)
(2) Front SAM unit (I think the SAM unit sends a signal to the alternator telling it to charge the battery)
(3) Dodgy connection between alternator and battery
(4) Battery (unlikely)
..anything else anyone??

 

[m7m]

Are you sure the battery you bought was of the correct rating? The alternator can struggle to charge a high rating battery.

 

[nippynoo]

The alternator can struggle to charge a high rating battery.

I dont see how. I would have thought that any alternator can charge any battery, it just takes longer, or shorter, depending on the Amp-Hours.

 

[Ted]

I dont see how. I would have thought that any alternator can charge any battery, it just takes longer, or shorter, depending on the Amp-Hours.

Correct.
And a faulty battery will not cause the charge light to come on.

My money would be on a faulty alternator - but I would definitely get it checked out.

 

[nippynoo]

My money would be on a faulty alternator - but I would definitely get it checked out.

I agree. Anyone know a way of checking a faulty alternator with a multimeter? Is it just a matter of measuring voltage across the battery with (A) engine off, (B) engine idling, and checking that voltage (B) is higher than (A)? Or does the front SAM need to coax the alternator into action as well?

 

[BlackC55]

The alternator pushes out 13.5- 14.4V when running. Any less than that the alternator is duff.

 

[Diesel Benz]

The alternator pushes out 13.5- 14.4V when running. Any less than that the alternator is duff.

How often would you say replacing the alternator regulator only would be sufficient instead of changing the whole alternator? Or is it not worth trying to save here?

 

[nippynoo]

Well, on my car (C220 CDI 2006), with same error message

Battery voltage after standing overnight is 12.40V
Start the car....after couple minutes...
Battery voltage at idle is 11.94V
Battery voltage revving car to 2500rpm is 12.20V
Battery voltage back at idle is again 11.95V

Now I'm confused. The alternator seems to be doing "something" at 2500rpm, but the voltages are so low.

 

[nippynoo]

Start the car....after couple minutes...
Battery voltage at idle is 11.94V
Battery voltage revving car to 2500rpm is 12.20V
Battery voltage back at idle is again 11.95V

Battery voltage when revving sometimes goes up to 14V, and drops back down when engine speed drops. So the alternator is doing something, intermittently.

Does anyone think it could it be a bad connection? Or is the rectifier/regulator more likely? Thanks

 

[BlackC55]

You have a duff alternator IMO

 

[nippynoo]

You have a duff alternator IMO

I've read that 99% of the time that alternators get taken out and tested the fault is not in the body of the alternator but in the regulator/rectifier/brushes pack that is bolted to the back of it. This makes sense because the alternator after all is just a coil of wire and some bearings. All the unreliable bits are in the regulator pack. In my case, the charging is intermittent (sometimes does 14V) so it points to bad brushes (maybe one is stuck, or they're gunked up)

Apparently its possible to replace the regulator (around £50) without first removing the alternator. Anyone know if this is really possible? Has anyone done it?

 

[Ted]

As per another post, my experience is from years ago, so take this advice with a pinch of salt.

The most likely part to fail is the regulator, as this contains delicate electronics in a hostile environment. The alternator also contains rectifier diodes, but these are generally pretty robust.

Older Mercedes with Bosch alternators commonly had problems with the regulator failing - the symptoms of these were that it would overcharge. A change of rectifier (with new brushes attached) would always cure the problem. This was held on to the back of the alternator with two screws, and if access permitted could be removed in situ, but I would always advise to disconnect the battery, as a slipped screwdriver/spanner in that area could short out the main live feed to the alternator.

As I say - not sure just how relevant this is to a 'modern' alternator, but if I were in your shoes, I would give a new regulator a punt.

 

[nippynoo]

CDI 220 2003 hi, jus wondered if anyone has any ideas what is causing my battery/alternator red warning light to flash on

I found it useful to display the battery voltage whilst driving. Before starting, turn the key one click to position 1 (engine off), make sure the display shows mileage, and then press the mileage reset button (on left of speedometer) 3 times, the display now shows battery voltage. Then keep an eye on the voltage immediately before the red warning message appears.

Mine is typically at 11.5V (after starting), then randomly every few minutes jumps up to 12 or 13V (alternator probably kicking in for couple of seconds), and then drops down to 11.7V. This sequence can occur at any engine speed, but is always followed immediately by the battery/alternator message.

 

[nippynoo]

As per another post, my experience is from years ago, so take this advice with a pinch of salt.

The most likely part to fail is the regulator, as this contains delicate electronics in a hostile environment. The alternator also contains rectifier diodes, but these are generally pretty robust.

Older Mercedes with Bosch alternators commonly had problems with the regulator failing - the symptoms of these were that it would overcharge. A change of rectifier (with new brushes attached) would always cure the problem. This was held on to the back of the alternator with two screws, and if access permitted could be removed in situ, but I would always advise to disconnect the battery, as a slipped screwdriver/spanner in that area could short out the main live feed to the alternator.

As I say - not sure just how relevant this is to a 'modern' alternator, but if I were in your shoes, I would give a new regulator a punt.

Thanks Ted. I'm tending to agree that the regulator pack is all that needs replacing (In my case it probably the brushes which are attached) The price quoted by a local alternator company to remove the alternator and fit a new regulator and replace in car is £60 labour + £55 parts + VAT. So total job about £140. (And they've offered to load test the alternator before fitting back into car, just to make 100% certain)

 

[nippynoo]

Well I've just had the job done and picked the car up. It was the regulator after all. The workshop let me see the alternator with the regulator removed, and the slip rings/back bearing were fine. So if you get the same symptons as me, and your's is a relatively low mileage (60k), then just replace the regulator.

Anyway the alternator now gives a nice steady 14.4 volts across the battery when the engine is running . Also the red battery/alternator message doesnt show any more.

The original battery was fine despite what Kwik-Fit said. I temporarily swapped it for another smaller one, so I could drive around, and put the original battery on charge for 24 hours. Its as good as new, giving 12.7V. So I'll put it back in tomorrow.

 

[mitch1981]

hi thanks for all replies, i've tried checking the volts on the alternator and its reading normal. 12v stand still 14.5v when engine is running, but for the 1st time y'day the car would'nt start then after 5mins in fired up ok. but there has been no signs of battery failure and when lights heaters and radio on the battery does'nt seem to get drained, so if its not the battery and if the alternator seems ok what other problem could it be, i should get it checked by computer but wondered if any one had an answer. thanks

 

[Ted]

Is the alternator light still flashing? If so this needs sorting first.
If this HAS been sorted, get an auto electrician to do a high rate discharge test on the battery before investigating any further.
Once these are eliminated you can look further.