Correct. Any car that originally came with the chrome, round button key, can accept a current triangle button key. The problem comes with the original all black first generation smart keys, that first appeared on the 1998 W210 and I imagine on the other models of that time as well.

Our 2008 ML320 only came with one factory (round button) key when we bought it used from our dealer in 2013. They gave us a replacement triangle key with the purchase, and my son uses it every day with no issues.

If 1 = black key, 2 = round button chrome key, and 3 = triangle button chrome key, then:

car originally equipped with key 1 will accept key 2
car originally equipped with key 2 will accept key 3

**amended per info from Shertex below**
but W210 cars originally equipped with key 1 will not accept key 3 reliably without replacing the EIS and both keys
However W211 pre facelift cars with key 1 will work with key 3

Actually the 1996-97 210s, the early W202s, and the W140s are in a worse predicament. These have blade keys, but have an embedded RFID chip, and the key blanks are NLA.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The original keys on my 98 and both 06's are all black, round panic button, no chrome....visually identical in all respects.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I'm pretty sure my CDI is a case of a car coming with Key 1 and then getting Key 3 as a replacement...I'm fairly confident that EIS wasn't replaced by PO.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Well that is good news. Maybe the issue is just with the first gen electronics in the W210 being incompatible with the later keys. Hopefully by CDI time they got it improved to where a new key will work in these.

So the 2005-2006 W211 got the all black key? They must have switched from black to chrome key at the 2006/2007 facelift transition then.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Yes. Both are 2006 and both came with all black keys.

You should see my drawer full of keys!

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I will say I had to order a new key for my 98 E300 and it is the new chrome with triangle button type. I get the start error every now and then mostly when the car has already been unlocked for a while and I try to start it. If car is locked and I unlock it with the remote, I usually do not get it. It usually happens to me when I stop the car and get out, then back in without locking and unlocking. I have found when I get the error, I pull key out, hit the unlock button on the remote and car flashed and vac pump runs like it is unlocking doors, put key back in and it works fine. Not sure what the deal is but this always seems to work for me.

Diesel W140s (and I think some of the other early ones) can use the same key as the w126 so those are still ok too (and a key costs $30).

I was quoted $1011 to replace EIS and that was with reduced vintage labor rate. However we have had many starts now with no issue so I might just keep going and see if the key and EIS continue to work for me or if they continue to fail I will replace the EIS

So you have not replaced the EIS and just have been dealing with the random no start? I am sort of leaning towards just dealing with the problem and not forking over $1000 for a new switch. I know it happens to my wife more than to me, and I also know that I lock the doors more religiously than she does. So far though the key has always worked sometimes after up to 4 attempts.

I did have codes read however and there is a current and stored code listed under the EZS portion of codes on our printout “the control module has open or short circuit.” The codes being B1156-004 and B1156-005. However I am still skeptical that those codes relate directly to the EIS. They are listed in the EZS section, but so are CAN faults from driver seat and CAN faults from lower panel control module. I had to pry info out of my service advisor at the mb shop too, asking for each and every page from the diagnostic scan. Isn’t there a diagnostic flow for each fault code that techs in workshops follow? Or do they just throw parts like I feel like they do😒. Anyone know? Former/current MB workshop techs?

That is correct. When it does it I just pull the key back out, hit the unlock button, then it starts.

When it happens can you turn key with dash and all working just no crank? Did you ever have codes read because of this?

Yes, key still turns and I get a red start error message on the cluster and engine does not turn over.

I have not gotten any start error messages when it happens in my 98, not sure what that means for my situation.