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Symptoms of Failed Alternator/Battery

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Symptoms of Failed Alternator/Battery


Old 08-13-2018, 01:17 AM
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1990 500SL, 2005 C55, 2006 M5
Symptoms of Failed Alternator/Battery

(134K miles on the car) I was on my way to Portland for a weekend road trip and my C55, while on the highway, had the red Battery/Alternator Visit Workshop message come up on the dash. My headunit powered off as did the A/C. I pulled over to the shoulder of the highway to figure out what to do for a minute. I decided to drive to the exit ramp as there were signs for a gas station at the next exit. I don't remember if I switched off the car or kept it running when I pulled over, but I immediately noticed that the car would not shift out of 1st gear. So I kept the revs below 3000 RPM, turned the hazards on and made a move toward the gas station. I made it to the exit ramp and to the intersection near the gas station, but then I noticed the coolant temperature gauge was creeping up, so I pulled over short of the signal light at the intersection and switched off the engine as I did not want to ruin it. I did a quick visual inspection of the engine while I was waiting for the engine to cool down and started making my plans for a tow truck back to Seattle. The drive belt looks good/ is not missing. After the engine cooled down, I restarted it and moved the two blocks needed to make it to the gas station. I eventually got a tow on a flat bed back to my apartment in Seattle. Then I drove off the tow truck ramp and got it into the parking garage ASAP.

I am a bit confused by what happened. It's one thing for the alternator to fail, but if the belt was still being driven and thus turning the water pump. would the engine in a C55 still overheat? (It was ~75+F ambient.)
I know that the cooling fan on the C55 is entirely electric with no mechanical clutch. If my battery was so dead that it caused the radio to turn off and A/C to shut down, how was I able to restart it several times after the first warning? This makes me think the battery is fine, but the alternator could still be bad.
First, I plan on thoroughly cleaning the battery connections.
Then, I plan to test the belt tensioner in case it is not applying enough pressure to the drive belt. (slipping belt, water pump not going at 100% is the idea here)
Last, I plan to get a new alternator assembly / or voltage regulator and replace it.
Battery is 1 year old.

Any other tips/advice, or solution if you have experienced the exact same thing, please let me know!
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Old 08-13-2018, 04:14 PM
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2005 Mercedes Benz C55 AMG..1967 Lotus Europa..1987 Lotus Turbo Esprit HCI..2006 Mercedes Benz E350
Hi....Had a similar situation happen to my 2005 C55. Played a round of golf and started to ride home (50 miles) and the same workshop warning light came on and I figured it was the regulator since instrument lights, tach, radio were working erratically. That might be the cause of your faulty rising temperature, too.

Called my buddy who's a mb dealer tech and he said "its more than likely the voltage regulator so just drive it home. It'll be ok!" So, I drove it home and next day removed the alternator, bench tested and found a defective diode. Bought a new regulator, installed it and it is just like it never happened!

Have yours tested asap and, hopefully, that's the solution!

Good luck.....

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Old 08-15-2018, 12:40 AM
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2004 C32
I had a similar experience with my C32. The red "check battery/alternator" would come on randomly for about 2 weeks. Sometimes in the middle of driving, sometimes upon start up, sometimes never at all. I finally had a similar situation to what you described. Things started turning on and off. Dash lit up like a Christmas tree. One crazy thing I noticed was the ambient temp was reading over 170 degrees F. I pulled over as you did, turned the car off and called the MB roadside. After about 10 minutes and them offering a tow, I realized I was about 1 block from the dealer and was able to start the car and drive it to the dealer. The whole car died right as I pulled into the service bay.

I left the keys in the dropbox and they replaced the alternator for a grand total of $1346! Wish I had known about the regulator back then. Bottom line, these cars do some funky things when the battery/alternator acts up.
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