Mercedes can't take the Texas heat - alternator problems?
Thread Starter
Junior Member
Joined: Jul 2010
Posts: 59
Likes: 0
From: Austin, Texas
2003 Mercedes C240, 2009 Audi Q5
Mercedes can't take the Texas heat - alternator problems?
Hi folks,
For a couple of years, I've had a strange intermittent issue with my 2003 C240. This is a low milage (58K) car that is well maintained. I get an Undervoltage warning that tells me to turn off consumers. Initially, I thought it was the battery, so I replaced it. A few months later, it happened again, so I took it to a MB specialist in Austin, Texas. They couldn't figure it out as they thought the alternator and battery tested fine. They ended up slightly increasing the idle RPM using STAR and I thought the issue was gone.
The problem seems to reoccur every so often and I made a correlation to the ambient temperature. The closer to 100 degrees, the more often it occurred.
Recently, it's happening quite frequently as the weather has been hot. I put the car in diagnostic mode and start it up. Voltage hovers around 13.3-13.5. As the car warms up, the voltage starts dropping. The hotter it is outside, the quicker the voltage drops. Usually it hits 11.7V or and the undervoltage warning pops up, typically within 5-10 minutes of running the car. I tried turning off AC, radio, etc. and it doesn't seem to help the voltage at all.
Any thoughts? My hunch is that the regulator is on the way out, but would love to hear from you folks.
Thanks!
For a couple of years, I've had a strange intermittent issue with my 2003 C240. This is a low milage (58K) car that is well maintained. I get an Undervoltage warning that tells me to turn off consumers. Initially, I thought it was the battery, so I replaced it. A few months later, it happened again, so I took it to a MB specialist in Austin, Texas. They couldn't figure it out as they thought the alternator and battery tested fine. They ended up slightly increasing the idle RPM using STAR and I thought the issue was gone.
The problem seems to reoccur every so often and I made a correlation to the ambient temperature. The closer to 100 degrees, the more often it occurred.
Recently, it's happening quite frequently as the weather has been hot. I put the car in diagnostic mode and start it up. Voltage hovers around 13.3-13.5. As the car warms up, the voltage starts dropping. The hotter it is outside, the quicker the voltage drops. Usually it hits 11.7V or and the undervoltage warning pops up, typically within 5-10 minutes of running the car. I tried turning off AC, radio, etc. and it doesn't seem to help the voltage at all.
Any thoughts? My hunch is that the regulator is on the way out, but would love to hear from you folks.
Thanks!
Member
Joined: Dec 2012
Posts: 220
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From: Houston, Tx, USA
2002 c240
I live in Houston. When I go somewhere and its 95-100, and leave it in a parking lot for 1+ hour, the only problem I have is the dashboard LCD just doesn't even come on until the insides get a little cooler. Do you keep your car in a garage?
Thread Starter
Junior Member
Joined: Jul 2010
Posts: 59
Likes: 0
From: Austin, Texas
2003 Mercedes C240, 2009 Audi Q5
It's normally garaged, but been outside for a week or so as I'm working on a garage project. It has been worse during this time, so perhaps it's heating up the failing component, whatever that might be.
