The advantage with an AUX-capable radio is that the head unit will display "Aux" as a separate selection from the CD changer. An undocumented (as far as I know) feature is that pushing the CD 1 through CD 6 selection buttons in AUX mode changes the input sensitivity of the auxiliary input.

If you don't have the CD changer, then using the changer input for an auxiliary input would work, except... The radio sends an "are you there" signal to the CD changer and expects a response. If it never gets one, you won't be able to select the CD changer. If the head unit did receive a response but then doesn't receive any further responses, you'll get a "CD Check" error on the head unit.

A number of 3rd-party interface vendors provide adapters that respond to the head unit polling and pretend to be a CD changer and have inputs for an auxiliary device. I know of at least one that lets you use a CD changer at the same time. You select whether you want the CD changer or the aux input via a number of keypresses on the head unit.

I have an 09/2002 build 325xiT (first week of model year 2003 production) and the factory wiring harness had an error where it wouldn't recognize the genuine BMW auxiliary input adapter. Two of the pins were swapped in the wiring harness behind the NAV screen.

If you're connecting directly to the pins on the BM53/BM54 radio, that shouldn't be a problem.

Note that different BMW production facilities phase in part changes at different times, depending on inventory. If a feature is listed as being available at the start of a model year, all vehicles of that model year should support it. However, a slightly earlier build from near the end of the previous model year may also have the feature. If the factory ran low on a particular part, they'd order the newer one rather than more of an older one discontinued by the component manufacturer. In the specific case of the AUX input, I have direct experience with this - a friend had an 08/2002 (2002 model year) BMW and I was able to install the AUX input cable in his car and it worked with no changes.

k, so what does NG, BM53 and BM54 stand for? At this point its either a coin toss to see if someone on the 5 and X boards is willing to maybe just swap decks w/ me if they never plan on adding aux input, or just go aftermarket and be done w/ factory stuff just like I have in every other BMW I have/had. What year specifically do I need a stereo from, or what model # ranges? I though I was good to go w/ my own deck since it has software version 50, but I guess I'm just stuck going another route Also, what years specifically were capable of playing MP3's? This sucks...i still want to see if there is a way around this, but I'm getting impatient also. This is the second trip to Seattle i'll be taking...and I'm stuck w/ old cd's or crappy stations in the meantime.

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NG = New Generation
BM = Bord-Monitor (radio designed for use with nav system)

I'm not seeing any of this written on any labels on my deck. What year did the decks start becoming MP3 compatible, i'm hoping maybe I can find someone on here who just doesn't care about aux input and see if they're willing to swap decks.

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09/2005 - the date when BMW I/K-Bus radios and CD changers got the MP3 functionality

Two other things:

- I was previously pretty careless despite checking AUX-in adapter few times. This weekend I checked again the wiring of my home made AUX in input and found the fault. I soldered wrong pins of resistor and capacitor together the way one of the capx blocked Left-to-Right pins connection and that is why no AUX IN adapter was detected. NOW IT WORKS PERFECT! Button "CD 1" selects the lowest sensitivity (lowest volume), button "CD 6" selects the highes sensitivity (highest volume at the same volume of input signal) to the input signal.

- During search for newer BM54 radio I noticed this information. The say is that all radio versions have the same hardware, they just differ by support for various features based on radio firmware fitted. So to have MP3 support at Your BM54 radio You just need to reflash main 29F400 program memory IC (and if it is not working then Serial EEPROM and DSP-PROM as well) on radio mainboard. Then, If You have MP3 capable CD changer and Mk4 navigation unit with firmware from CD V27 or newer, You got it!

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Despite driving Xs´smaller brother E46/3, still having a lot in common ...

I have a 2006 X5 with DSP and Mark IV NAV.
If I hook up an aux input at the back of the in dash unit I should be able to use my factory CD changer as well correct ?

Correct.

Who ready for it?

Finally! A Pre-2002 Business CD AUX Input HACK!!!!!!