Last week my 2006 C55 AMG showed a flashing heated seat light in the morning on the way to work. Defrost flashing too. I didn't know what the issue was but I was able to get to work. About 20 minutes after getting to work I tried to move my car and it wouldn't start, slow crank. No warning lights. I didn't know what the deal was but this car is only 3 months new to me so I figured I'd just replace battery and go from there. Swapped for a new Weize 49 AGM and same thing, but going home I noticed about 20 minutes into the evening ride that my SRS, and some lights came on, then it was red, alternator or battery warning and within 3 miles my headlights shut off. I stopped at a gas station, car was spitting and sputtering . A friend came and charged the battery for me for 10 minutes and I was then able to limp home.

So I figured I needed an alternator but here noticed people changing the voltage regulators and decided to try my luck. Took several hours, still nearly had to completely remove the alternator but finally got it sideways so I could get the regulator off and take a good look at it. The old one was fully intact and contacts were 2/5's of the new regulator. I swapped regulators and put it all back together. Few hours later was ready to start and hopefully charge. Nope, no dice. Started car and the red batt/alt service warning immediately came on. I'm at a loss.

Am I missing something? Can I test output from the alternator from the jump terminals near battery or am I overlooking something? I'm not sure what else to test and I'm afraid I'll buy a $400 alternator and the same outcome will happen. Any advice? I have a multi meter and just picked up a Bluetooth ODB2 reader but haven't gotten home yet to plug it in and see if it surrenders a path to victory?

Any help would be greatly appreciated.

Thanks for looking.

 

Test output of alternator at the lug on the alternator, if it’s not 13.7 or higher when running, then it may be one of the diodes in the alternator. If it’s 13.7 or higher, check the battery voltage. It should be the same as the output of the alternator. If not the wire or fusible link in the wire is bad.

 

Get it sorted quickly. Low voltage wreaks havoc on electronics.

 

On left is cheapo voltage regulator found on re-manufactured alternators. On right is Bosch. Note difference in heat sink.

 

From some search in the web it says the flashing of heated seat red light is indicator for low voltage. As others indicated check to see if your alternator is charging, if not then you need to check to see if you have a parasitic load somewhere

 

Can the C-class pull up and display the voltage on the electrical bus on the instrument cluster as is possible on the E-class? If yes, pull the voltage up on the instrument cluster and observe. I do not know so that is why I am asking the question.

 

I seem to remember that it can, I bounced around it at some point on my C55.

 

Push the little round pin to the left on the cluster in front of you 3 times while the ignitionkey
is in 1:st or 2:nd position and in miles position in the cluster. You will hear a "beep".while in that position.
Then scroll with the steeringbuttons on the left untill you see the voltage.
You can then start the car and see your voltage when the car is running and see the difference.

You can also see the oil level when in that position when you turn the key another notch if you start
the procedure from scratch.