Hi everyone! I have a quick question that hopefully you can all re-direct me to the correct conclusion.

For the past month, my dash lights up with "Visit Workshop" and displays the red battery icon along with the message, "Battery protection convenience functions temporarily unavailable". When this happens, my car (2003 E55 AMG), drives normally but the A/C, heated seats, and interior lights do not work.

However, this message DOES disappear after I drive the car for a while, turn off the car, and then turn the car back on; then everything resumes to normal.

I've read numerous threads on here that explain the parts that would cause this to occur and I can tell you all the parts that I've replaced thus far:
- Main trunk battery
- Auxillary battery
- Auxillary battery relay
- Alternator

I was reading a thread on this forum that said if all the above parts are functioning correctly, the culprit is the battery control module in the trunk.

Before making that purchase, I want to make sure that this part would solve this issue.

Any and all comments would be greatly appreciated!

 

You're sure your aux battery is good? And your main battery? Those are first things to check before expensive modules. If either battery is more than a couple of years old, I'd replace it or them first.

 

Yes. I replaced those two last week. The alternator was replaced in November 2019 and the auxillary battery relay I changed yesterday.

 

Sounds like time to replace the BCM. As to your question, there are never any guarantees. It could even be a wiring issue (make sure all battery connections are clean and tight) but the BCM is the best guess at this point.

 

I appreciate your input. Thank you!

 

Update: I just changed the Battery Control Module (along with the other items I listed above) and the dash STILL shows me the “Visit Workshop” error code.

Any thoughts on what else it could be?

Should I just take it to Mercedes and have them diagnose it?

Any and all suggestions regarding this issue are welcomed.

 

Have you read this thread? Long story is that someone reversed the battery cables when jump-starting and burned out a 150A fuse, with similar symptoms to yours. $9 fix.
https://mbworld.org/forums/e-class-w...-9051-a-3.html

 

Thank you for this thread! I found the entire unit on eBay for about $25. I’ll give switching this out a shot since it’s inexpensive.

Hope it works!

 

Hope so too. Make sure you check the 150A fuses for continuity. At that price I assume it's used so you can never be sure. If you don't have a multimeter at least visually inspect the fuses. Or get a meter.

 

I checked the voltage of both the 150A fuses and the meter was showing 12V for both. I'm thinking it could possibly be the capacitor located inside.

 

Voltage at the fuses doesn't really tell you anything. There should be zero volts across each fuse. Only way to be sure is to disconnect wire on one side of each and measure resistance across the fuse. Should be 0 ohms.

 

I had red battery warning and done all replacement parts mentioned, VR, BCM, aux & main battery, aux relay, & alternator...with no success. Finally an Indy shop suggested to change out the driver’s front SAM and that did the trick for my car. Good luck

 

Just curious if you ever found the problem?

 

Before I went ahead any deeper than I already was with finding a solution that seemed to have no end in sight, a friend of a friend suggested I bring the car to him as he has a lot of experience with AMGs.

He hooked the car up to the computer and after an hour, he told me it’s the alternator even though the alternator was producing 12V. So he swapped my 5 month old alternator with a new one and the error message went away and all the functions resumed to normal.

So I ended up returning all the unnecessary parts I had bought and now the car is running smoothly.

It was just so weird to have to change the alternator so soon AND even though it was putting out 12V.

 

12V isn’t quite enough. You need 13.5-14.5 while running

 

It was interesting because when I would turn the car on (cold start), it was outputting 12.3-12.5V. Then when I would rev it, it would jump to 13.9-14.0V and stay there after it had been running.

 

Good to know thanks!