This is from the Sept. 04 issue of startuned magazine at www.MBWholesaleParts.com

Well, there's good news and bad news. First,
none of the radios Mercedes-Benz has used for
years will lose their station settings from a
power interrupt, so the customer won't have to
tune or seek until he finds his favorite disk
jockeys, classical music stations, or talk shows,
then reset those buttons. But no matter how fast
you might be at realizing what you've done and
slapping that cable back on the terminal, you're
going to have to reset the code. This function
occurs in milliseconds. Rumors you may have
heard about internal batteries or lingering
capacitance holding this useful feature at bay
for any length of time at all are simply false.
You'll have to just accept it, then follow through
with what must be done to make that radio
operational again.
The radio will inform you of your mistake
with the alarm display, "CODE." After you're
done slapping your forehead, what do you do to
set things right and stay in your patron's good
graces? Well, resetting the radio is done in different
ways for the various audio systems found
in Mercedes-Benz cars, and here's the information
you'll need to perform the procedure on
some common models.
One note up front: Carmakers first installed
radio anti-theft systems to thwart felons and
bandits who ripped radios from cars, leaving
gaping holes in ruined dashboards. With antitheft
systems, this enterprise fails because such
a filch renders the radio useless, and although
junkies may wallow in delusion with the
shrieking gibbers, drug pushers and fencers of
stolen property do not. No way they're going to
pay anything for even the most upscale unit if it
can't be used because the thief neglected to get
the code card along with it (that's why M-B
advises that the card should not be kept in the
glove compartment, although after the owner
takes it out and puts it somewhere among his or
her other papers, there's a good chance that he
or she won't be able to find it again, human
nature being what it is). Nothing in this article
serves to get around that anti-theft feature. If
you don’t have the specific radio code for this
vehicle, either from the car owner’s records or
directly from Mercedes-Benz's C.A.C.

16
(Customer Assistance Center), you won ’t find it
here, either, or any way to work around it.
If your customer doesn’t have the radio-code
information, you’ll find that the company's representatives
will want a fair amount of proof of
who owns the car and who is doing the work
before they’ll release the unlock sequence. In
some cases, MBUSA may require that you take
the car to a dealership to confirm all the vehicle
information first. Considering that the whole
point of this system is to make things inconvenient,
if not impossible, for thieves, you can
understand why.
Mercedes-Benz builds cars, not radios, so
there are different radios in different cars,
depending on the model year, the accessory
choices and so on. Different radios use different
release code procedures, so make sure you
know which radio you have before you start.
You won’t destroy the radio by punching the
code in the wrong way, but you could trigger a
second level of defense, requiring a longer or
shorter wait depending on how often you’ve
flubbed the procedure. This second level of
defense could require leaving the radio turned
on (but non-functionally locked) for as long as
24 hours. The point, again, is to discourage and
dishearten those who believe in helping themselves
to others' property.
Unlocking the CODE
Start with the model year in our boxes below.
Make sure the radio faceplate in our line drawing
corresponds to the radio in the car, and follow
the instructions exactly. Many different
radios use slightly different unlocking procedures,
and you must use the exactly correct one
for that radio.
For earlier models, you may recall that there
were some "gray-market" cars with European
radios, none of which is included here. For
them, you’ll have to go to your local dealer (who
may not be entirely ecstatic about the job,
either). The first generation of anti-theft radios
to appear in Mercedes-Benz cars were the
Beckers used from 1986 to 1989. If one of these
early units requires digital unlocking, you’ll
definitely have to take it to an M-B dealer
because a physical electronic key is required to
unlock them, and these keys are not generally
available.
Avoiding the situation
Of course, you'd be better off if you didn't
cause this sometimes-frustrating glitch in the
first place. So, whenever you're about to disconnect
a Benz's battery for whatever reason,
stop and think. All you have to do is attach an
auxiliary power source to the cables. We used to
keep a small motorcycle battery around for the
purpose, but now we just use our portable
jump-start box. There's even a special tool available
called a "Memory Retainer." By the way, if
you plug the auxiliary into the cigarette lighter,
remember that you'll have to leave the key on to
keep Circuit 15 alive.
Radios from different suppliers have different
release code procedures. If you try the wrong
one, you might trigger a second level of
defence, which may entail a long wait.

Procedures for Selected Models

As of Model Year1991
Alpine Radios
Recording Sequence:
1. Turn ignition key to position 2.
2. Turn radio ON. "CODE" appears on the display.
3. Enter first digit of anti-theft code from CODE
card. "CODE" will disappear and the entered
digit will flash on the display panel.
4. Enter remaining three digits (total of four
digits). Verify that the correct code is flashing
on the panel. If wrong digit was entered, reenter
code until correct code is displayed.
5. Press button "*" to complete the sequence.
Radio will beep and resume normal operation.
If Unsuccessful:
6. If "HOLD" appears on panel, the radio must be
left ON until "CODE" appears. This may take
either 15 minutes, or 24 hours depending upon
the number of unsuccessful attempts made.
7. Once "CODE" appears, continue with step 3.
As of Model Year1994,
Alpine & Becker
Recording Sequence:
1. Turn ignition key to position 2.
2. Turn radio ON. "CODE" appears on the display.
3. Enter first digit of anti-theft code from CODE
card. "CODE" will disappear and the entered
digit will appear followed by four dashes.
4. The next digit to be entered flashes. When all
five digits are entered, the first digit flashes
again. Verify that the correct code is on the
display. If a wrong digit was entered, re-enter
complete code until correct code is displayed.
5. Press SC, Seek or Tune button to confirm code.
The radio will resume normal operation.
If Unsuccessful:
6. If "WAIT" appears on panel, the radio must be
left ON until "CODE" appears. This will take
either 10 minutes or 24 hours depending upon
the number of attempts made.
As of Model Year1999,
Becker Accessory Radio
Recording Sequence:
1. Turn ignition key to position 2.
2. Turn radio ON. "CODE" appears on the
display followed by four stars.
3. Enter first digit of anti-theft code from CODE
card. The first star will disappear. Enter the
remaining three digits. Each successive star
will disappear as the code is entered.
4. The radio will resume normal operation
if the code was entered correctly.
5. If an incorrect code has been entered,
"CODE" and four stars will reappear on the
display. The correct code must be entered.
If Unsuccessful:
6. If three unsuccessful attempts are made and
"WAIT" appears on panel, the radio must be
left ON until "CODE" and four stars appear.
This will take 60 minutes.
7. Once "CODE" and four stars appear,
continue with step 3.

Up to Model Year1999
Model 163 Premium Radio
Recording Sequence:
1. Turn ignition key to position 2.
2. Turn radio ON. "CODE" appears on the display.
3. Enter first digit of anti-theft code from CODE
card. "CODE" will disappear and the entered
digit will appear followed by four dashes. Enter
the remaining four digits.
4. Press the < or > button to confirm code.
Radio will resume normal operation.
5. If an incorrect code has been entered and
confirmed, "CODE" will reappear on the display.
The correct code must be entered.
If Unsuccessful:
6. If three unsuccessful attempts are made and
"WAIT" appears on panel, the radio must be
left ON until "CODE" appears. This will take 10
minutes. If three more unsuccessful attempts
are made and "WAIT" appears on panel, the
radio must be left ON until "CODE" appears,
which will take 60 minutes.
7. Once "CODE" appears, continue with step 3.