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Adding AUX Input to 02-04 Subaru Impreza WRX 6CD Changer [86201FE120]

2020.04.11 ｜ Yuki Rea

The 2002-2004 Subaru Impreza WRX models equipped with the 6 disk CD changer (Subaru Part Number: 86201FE120) do not have any way to accept an auxiliary audio input from the factory. This mod will tap into the stereo audio output of the cassette amplifier IC before it reaches the main amplifier. Inputting our signal here allows us to use no additional filters or circuitry. The signal will not be processed by the cassette amplifier which means audio quality will be untouched and very clean. Any audio injected through this AUX input will be heard along side all other functions of the head unit including the radio, CD player, and cassette player. This is useful if you want to listen to the radio while still having the audio from a navigation system played through the car's speakers. The only downside to this modification is that you will need either a blank cassette tape or CD burned with a silent track to allow the unit to remain on and not output any audio.


Requirements for this modification

  1. Soldering iron
  2. Phillips/Plus screwdriver
  3. Audio cable of your choice
  4. Dummy cassette or CD

Optional recommended tools

  1. Lab bench power supply
  2. Solder wick and/or solder sucker
  3. Wire stripper
  4. Flush cutter
  5. Plastic tool for removing interior trim
  6. Speakers for testing

Disassembly

In order to preform this modification you will first need to extract the head unit from your car if you have not done so already. The trim piece around the head unit is held in with plastic clips, it pulls off with the aid of a flat screwdriver or trim removal tool. Unscrew the unit from the dashboard and disconnect all the cables. You will also need to disassemble the unit, the construction is fairly complex but not too difficult. The side pieces all interlock and have to be removed and installed in a specific order. There are also multiple different size of screws with different lengths, it is possible to damage the unit if a long screw is put into the incorrect hole. Take photos as you disassemble the unit to help you remember how each piece goes together and where each screw goes. The unit will need to be disassembled until you have access to the cassette player PCB as shown highlighted in the image below.



Modification

The only step to this modification is soldering your cable to the correct pins on the cassette board inside the unit. I recommend using some sort of strain relief on the cable such as using a cable tie to fix it to the inside of the metal chassis. Below is are schematic and board layout images depicting which pins on the PCB your cable needs to be soldered to. Note that not all audio cables use the same color code, I recommend using a multimeter in continuity mode to check which wire is connected to each pin on your cable. In my case I was using a 3.5mm female cable which had the following pin-out: [yellow=GND green=R white=L] I routed my cable just above the antenna connector on the main PCB where there is a hole in the cast aluminium heat-sink which is part of the back of the unit. From there I routed the cable above the unit to the pull-out cup holder which I replaced with a phone mount. I use a short male-to-male 3.5mm cable to connect my phone to the head unit.


Blank Media

In order to allow the head unit to stay powered on and accept the auxiliary audio input, a silent CD or cassette must be used. I prefer to use a cassette as I like to keep my CD changer loaded with disks. I used a cheap cassette to 3.5mm adapter which I removed the cable from and lubricated the gears to eliminate gear noise. You may also be able to use a blank infinite loop tape, I am not sure if the tape head would pick up noise from the blank tape however. The best option to ensure no noise would be to use a silent CD. This can be done by burning a silent audio track which spans the entire disk and setting the head unit to repeat.


Testing

I recommend testing the unit while it is still disassembled on your bench before installing it in your car. I used my DC power supply and a set of speakers which I connected to back of the unit with small test leads. Below is a pin-out diagram of the 14 pin connector, note that both pin 6 and pin 10 need to be connected to 12v in order for the unit to power on. Ensure that both right and left audio channels are present and that they are not reversed before assembling the unit. There should be no noise and the signal should be the same quality as if you were listening to an audio CD. If there is noise, the signal is weak, or you are having other issues, double check that you have soldered the connections to the right pins and test again. You should not need to remove the cassette amplifier from the circuit, if you still have noise you can try using a ground loop isolation transformer but I have found this not to be necessary.

  1. Illumination [+]
  2. Front Speaker [R+]
  3. Front Speaker [L+]
  4. Rear Speaker [R+]
  5. Rear Speaker [L+]
  6. Power [B +11-16v]
  7. Illumination [-]
  8. Front Speaker [R-]
  9. Front Speaker [L-]
  10. Power [ACC +11-16v]
  11. GND
  12. Rear Speaker [R-]
  13. Rear Speaker [L-]
  14. Antenna Motor