glenrhoades

Hi Everyone -- newbie here.

The battery light came on in my 2002 C240, so I installed a new battery and had the alternator checked (checked out OK). The battery light still flashes intermittently. What should I change/check next?

samaritrey

Time to get the volt meter out and see what it does

glenrhoades

Went to a little over 14 at the battery shop last night. I will check myself tonight after work. What should it be?

Moviela

Just after you start the car it should be as high as 14.4 volts on the battery terminals. When the motor is stopped the terminal voltage should be 12.5 volts. You can read the voltage, labeled Ub in the MFD (Multi Function Display) using the "Dyno mode." The voltmeter is built into the front SAM.

Did you buy a genuine Mercedes battery? Without the 100Ah rating, aftermarket batteries are just too limp to handle the needs of the car.

You might have a slipping belt. You should have changed the tensioner, belt, and idler by now. The spring in the tensioner becomes limp over time. Without the proper tension on the belt it can slip on the alternator pulley. Pelican has the OEM parts for about half the dealer, and it takes 45 minutes to install for a first timer.

glenrhoades

I bought a duracell procell gold with 900cca. Hopefully that will work.

I bought the car used a few years ago, so I do not know if the tensioner, belt, and idler were changed. I will check them tonight also.

Thanks

glenrhoades

Checked alternator again - 12.85 not running, 14.52 running

Moviela

I wish battery sellers would stop advertising Cold Cranking Amps as it is a rather meaningless specification. It is like telling you tires are black. The real specification of interest is the Amp hour rating. Duracell seems intent on concealing that number. Few batteries meet the Mercedes spec of 100Ah. Since W203 were built the battery business has changed the design to a new type called AGM. The best of those are of silver/calcium. A DIN H8 size 49 comes flooded or AGM. The flooded has a 100Ah rating, and the AGM is 95Ah. The AGM has some advantages even though it has 5 less Ah. Porous separators lower resistance and increases power. They are also truly maintenance free.

These batteries should weigh 56 to 58 Lbs. Real men are heard to utter "Jesus" when lifting the battery into the car.

The voltages you report are quite good. You flashing warning might be a loose or dirty connection on the battery or the alternator. Dirty brushes in the alternator could be the problem. Make sure the battery terminals are clean and shiny. Check the cable between the engine and ground. The fat one. Make sure it is clean and tight.

Boom vang

I had a similar problem, the light came on and since the battery was almost 8 years old I assumed it was the battery and changed it with an OEM battery. The light was still on and despite no problems in charging and giving output to specs it was the voltage regulator that caused the problems and threw the message. There was an issue with Valeo voltage regs in early C classes and they don't stand the test of time.
Best place to buy these parts is http://www.americanenginesco.com/ way cheaper than at the dealer, I replaced mine for $55 and a hour and half of my time.

I am willing to bet it is the VR that is causing the problem

samaritrey

Just replaced my Valeo Alternator at 199,700 miles. The VR went out and I decided that even though the bearing and center post were in perfect shape that it was time to just replace the whole thing.

Curious what the issues with the Valeo VR you are talking about were?

glenrhoades

Thanks Boom vang. I will replace the VR. Are there any threads or videos on how to change it?

glenrhoades

Well, what manual would everyone recommend I buy? Are there any good online resources?

Boom vang

if you search on the forum there is a DIY somewhere, here is one to start

https://mbworld.org/forums/c-class-w...-diy-boys.html

glenrhoades

I finally changed the alternator yesterday. As mentioned earlier, I got a new battery the moment I 1st saw the battery/alternator light. The battery/alternator light continued to come on, but only about once a day and just flashing for a few seconds then going away. Since the alternator numbers looked good, I just assumed I had a loose connection somewhere and just kept driving it. Well, I was driving Saturday and the light came on, but did not go away. A little later, all electrical shut down -- no air, blinkers, windows, transmission shifting, nothing. I shut it down and it would start right up, but no electrical at all.

I had it towed home and replaced the alternator and belt yesterday. $250 in parts and about an hour to do the job. Started right up, no more warning/error light and runs perfect. I was pretty dumb to not just do this a month ago. Lucky I didn't screw something else up.

VVF

You got a great deal then. New alternator from the dealer is about $800 in parts alone...

glenrhoades

Yeah, I got a re manufactured Bosch with a lifetime warranty and a nice aftermarket belt. I was pleasantly surprised with the price.

amoora58

The same problem happened with me . I had replaced the alernator ( valeo ) with new one ( Bosh ) and the warning light dad disappeared. I think there has been a defect in the altenator itself.

wvadam

Hi, I fought that problem for years, red light bat/alt. Mostly it came on when the weather was cold. All voltages were normal but I changed the battery and alternator anyways and still got the error. Eventually I just changed the front sam with a used one from ebay, about $75, and the error never came back. If you choose to do this make sure you check the sticker on your existing one and get exactly the same used one so you dont have to program it. This worked for me.

as a side note, I swapped my original bosch alternator with valeo and had no issues.

Roger161

2005 C230 Sport with 141K miles. Original alt / battery ( 10 years old ). For the first time, alt/bat red light should up at idle at a stop light. The car actually almost died at idle. Taking it in tomorrow to my mechanic to have it all checked out. This was after we performed a major tune up as well. Hoping for the best and to solve the issue tomorrow.

Icebreaker

I just replaced my battery 3 weeks ago, I had 130k on mine. I just replaced the voltage regulator but still has the light on. Waiting for a new alternator which will be here tomorrow. Mine is a Bosch alternator, I heard you should replace it with the same alternator part number otherwise you may still have the red light on.

Crna Mechka

That gave me a good chuckle.

This is what happens when you use the wrong battery in these cars. They end up costing you more than the OEM battery would.

OEM (or at least correctly rated reputable brand) or nada, just my 2 cents.