Hi All. My 2016 GTS shows current and historic codes B21DC01 and P172C13. There is no CEL and the car (including eco stop/start) seems all fine. Yet the codes are there and on clearing them seem to come right back.

I want to track this down, but need some basic info to start looking:

• Does the 2016 GTS have an actual aux battery, or does it use the capacitor-based system to provide the needed aux supply?
• Where is the location of the aux battery (if it has one) or the capacitor part (if it does not)?

This vehicle gets driven very little, but is always left on the Mercedes-supplied maintainer.

Any suggestions from the wise out there as to where to start looking or diagnostic procedures?

Many thanks!

 

There is a TSB on it. I don't have access to this TSB, but why don't you see if you can get a copy of it. It should be thoroughly revealing how to fix it.

https://www.tsbsearch.com/Mercedes-B...54-19-P-061447

 

Thank so much for the note. I did see reference to this TSB in my searches before posting, but all the links I found did not show the actual TSB, only the summary information.

I will keep looking for the TSB, and if anyone has suggestions on where I might get a copy (or can answer the original question about the auxiliary battery or capacitor part) that would be wonderful.

Thank you again!

 

You're welcome.

Maybe try reposting in the tech forum. Sometimes MB techs show up there, might be able to snag the TSB for you:

https://mbworld.org/forums/mercedes-tech-talk-41/

 

Thank you - I will do that now!

 

Sadly no one has responded to my plea for a copy of the TSB on the technical forum. So time for me to try the next step.

Is anyone able to answer the following to help get me started:

• Does the 2016 GTS have an actual aux battery, or does it use the capacitor-based system to provide the needed aux supply?
• Where is the location of the aux battery (if it has one) or the capacitor part (if it does not)?

Many thanks!

 

So, regards the aux battery, a VERY FEW of the VERY EARLY GTs had an aux battery, then all switched to capacitor. If you have the aux battery it will be located in the hatch, left side behind the cover that reveals the rear fuse panel. The battery will look like this:

 

Excellent - thank you! I will check!

 

I did a little work in my WIS. I can provide you with some data that might help you solve your issue. Without the actual TSB though, I cannot offer much in where to start. The TSB is obviously specific and it is just guessing w/o it. Hope this helps you.

These are the charging circuits:



These are the module IDs on the Canbus:






If I was a wilda$$ gambling man (and I'm not), I would probably spend a little time around F32; F32K2; R62; N73 too, to start...but gambling is gambling and has its odds....

 

Murray,

I've reread the faults you first posted and I know you're pursuing an aux battery or capacitor. I am thinking your problem is a fault in the ignition lock. Same thing, the TSB would tell all, but now, if it were my issue I'd be focusing on the ign switch N73.

Here is a function flow of N73, and a flakey pic of the circuit diagram.



Circuit


I have a spare ign lock from a 16 GTS, but I don't know its status. It might not be good, but here is at least a P/N for you. If you have to replace it, the entire glove box has to come out. I've done that so I can walk you through it if you need.

Here are some pics of the switch for reference:




I am not certain, but if the ign is faulty, I don't think MB sells it BC of security (only to dealers), and I think it needs to be coded into the network.

 

Acta (apologies - I don't know your name) - this is a massive help. Thank you. I had no idea this could possibly be the ignition switch. I have not used the switch in the past, but I suppose the first thing to try is to see whether I can start the car with the key. If not, that would be pretty telling. And as an aside I did check the location you kindly provided to confirm I had no aux battery - and indeed I do not have on in that car. I just replaced both the main batteries and aux batteries in my S and E - so when the code came up on the GTS, I think I immediately went there.

I will head down today to try out the ignition switch and report back.

It's very kind of you to make this effort to supply me with this info - you've put me miles ahead of where I was before knowledge wise - so very much appreciated.

All the best and I'll report back.

 

You're welcome,

Acta is fine.

The first thing I would try is just what you're doing. Insert the key and try all the positions including a start. The fault calls out an "open circuit"

Some simple checks, following the circuit schematic above -

There is a direct connection to the front SAM (N10/1) and the front door module (N69/1). A really fast check on the door circuit, just open the driver's door and the start button should light. I checked that on mine. If you are not getting the start button to light that would be an open circuit (for example).

 

Hi Acta,

Absolutely a must. The "ignition lock control unit" is married to several control units (bigamy !!!) and belongs to the driving authorization system (FBS 4 = Fahrberechtigungsystem Generation 4)

Best regards

Stenzel

 

Thanks for this again. I just did a quick check and all good on the use of the key and the lighting of the start button. In fact, aside from the code on the scanner, I can't detect any fault.

I will start looking a bit deeper and if all else fails, will take it to the dealership at least for a diagnosis and go from there.

Thanks to you (and Stenzel) for your kind help!

 

Hi Stenzel,

Yes, and that is a big reason I'd like to see the TSB. I've tried all my sources. It could be if it is an ignition fault the TSB has security information that would be off limits to the public.

Murray,

Glad you were able to do a few simple tests that should make a list of possibilities a little shorter. Wish I could be more helpful, but issues like this are so difficult to solve online.

All the Best,

 

(sorry to revitalize an ancient thread)

I've got the same set of codes on my 2020 GT-C... Murray, did you ever get these codes resolved?

Thanks!

B

 

Was there ever a resolution to report on these error codes? I'm getting them on my 2019 AMG GT and all positions on the key module work just like the OP.