hamodi
Active Member
- Joined
- May 22, 2016
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- Your Mercedes
- W221 2007 S320L CDI
Hi everyone, have a 2007 W221 S320 CDI with 62k miles. Big auxiliary battery in boot went flat for 1-2 weeks as car had engine problem and was left unstarted as being repaired for 2 months. Car running again and starts and drives fine for past few weeks but I am intermittently getting the red battery symbol showing on the dash. So I entered the secret menu so I can monitor the battery voltage as I'm driving to see what's going on:
UB Voltage when getting into the car first thing in the morning is 12.2V. When I put the key on the voltage drops to 11.3V as the fuel pump primes then goes back up to 12.2V. Car starts and alternator kicks in and raises the voltage to 14.4V.
During my 50 mile commute, about 2-3 times the battery symbol will come up and just before it does I notice the 14.4V suddenly drops to 12V. On most occasions it will kick back in and rise to 14.4V after a few seconds but a few times it has taken about 3 minutes and my voltage dropped to 11.7V in the meantime. Even after my long commute, when I turn the car off, the voltage drops to about 12.2-12.3V.
Other things to note: I have taken the auxiliary battery out and it's still the battery from new (manufactured 2006!). Also, I had an oil leak from bank 1 rocker cover which may have gone on the alternator as it's located nearby. Car starts fine, reliable and all electrics in car working fine despite issue of battery warning light.
I would change the battery, as the voltage drop doesn't seem right, but I'm just worried it might still be serviceable and bad voltage regulator or alternator from oil leak is causing me the battery light as its dropping from 14.4V to 12V. Or maybe the alternator is cutting out as the battery has dead cells/short circuit - don't know if it's programmed to do this?
Any advice from anyone would be appreciated. Thank you.
UB Voltage when getting into the car first thing in the morning is 12.2V. When I put the key on the voltage drops to 11.3V as the fuel pump primes then goes back up to 12.2V. Car starts and alternator kicks in and raises the voltage to 14.4V.
During my 50 mile commute, about 2-3 times the battery symbol will come up and just before it does I notice the 14.4V suddenly drops to 12V. On most occasions it will kick back in and rise to 14.4V after a few seconds but a few times it has taken about 3 minutes and my voltage dropped to 11.7V in the meantime. Even after my long commute, when I turn the car off, the voltage drops to about 12.2-12.3V.
Other things to note: I have taken the auxiliary battery out and it's still the battery from new (manufactured 2006!). Also, I had an oil leak from bank 1 rocker cover which may have gone on the alternator as it's located nearby. Car starts fine, reliable and all electrics in car working fine despite issue of battery warning light.
I would change the battery, as the voltage drop doesn't seem right, but I'm just worried it might still be serviceable and bad voltage regulator or alternator from oil leak is causing me the battery light as its dropping from 14.4V to 12V. Or maybe the alternator is cutting out as the battery has dead cells/short circuit - don't know if it's programmed to do this?
Any advice from anyone would be appreciated. Thank you.
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