How We Solved “No Audio” After Installing a CarPlay Module on a 2012 Mercedes C250

Last week, we had a customer who wanted to modernize his 2012 Mercedes-Benz C250 by adding a CarPlay module, it's a NTG 4.5 system. The installation process went smoothly—but after completing the wiring and connections, we ran into a problem: there was no audio output from CarPlay.

This issue is more common than many people think, especially on older Mercedes models without an active AUX input. In this post, we’ll walk through how we diagnosed and fixed the problem by activating the AUX Audio via the car’s engineering mode.

The Issue: No AUX Input Available

After installing the CarPlay module, everything displayed correctly on the screen, but no sound came through the speakers. We quickly confirmed that this wasn’t a wiring issue—the module was working fine.

The problem was with the factory system:

• The 2012 C250 did not have an active AUX input in its COMAND menu.

• The CarPlay module’s audio output relies on AUX mode to route sound to the car speakers.

The solution? Activate the AUX Audio through the car’s hidden engineering menu.

Step-by-Step: Activating AUX Audio in Engineering Mode

⚠️ Disclaimer: Engineering Mode is intended for trained technicians. Please proceed carefully and do not change unrelated settings. Incorrect changes may affect your COMAND system.

1. Access Engineering Mode

1. Turn on the ignition (you don’t need to start the engine).

2. Press and hold the END CALL button, the # key, and the 1 key simultaneously for about 5–8 seconds.

3. The Engineering Mode menu will appear on your COMAND display.

2. Navigate to AUX Settings

       1.    Enter“Engineering Mode(1/2)”As shown below ；use your factory knob choose
              “7.HW Setting”and press Enter

        2. Select "7.7 HU Parameter"
 
   3. Enable AUX Audio

1. Change the AUX Input setting from “OFF” to “ON” (sometimes labeled as “Activated”).

2. Save and exit the menu.

3. If your “Audio Aux” is grey, can not be selected,  please continue following steps
4. Return to“7.HW Setting(1/2)”；select and enter“7.5 TGW Parameter”
5. Enter“7.5 TGW Parameter” select “(1) MOST    :off”as shown in pic 9；Enter to next menu and select“on”as shown in pic 10；
6. Under “7.5 TGW Parameter”menu Enter “(2) Audio Source :Internal amp”and then select “External Amp”as shown in Pic 13 and 14
   Please note: after you choose External amp and no sound for any audio source(FM radios,Bluetooth ect), please lock your car for 10minutes then switch on-Engineering Mode--7.5 TGW Parameter --(2)Audio Source— Internal amp

7. Return to step 5, Now you should select and enter” Audio AUX” as shown in Pic

   Please Note:   

   if your Mercedes equipped with factory Sirus XM radio. Make sure your 7.5 TGW Parameterà(4) SDARS is switched to Installed otherwise sirus XM radio will disappeared from your Command Audio Menu.

8.  Return to“Engineering Mode(1/2)”as shown in pic 15. Then use your Mercedes Knob push down to enter next page “Engineering Mode(2/2)

9. Select and enter “9.System Reset" then “Yes” to reboot your Radio
10.  Wait your radio to restart，get out of your car，then lock your car for 10minuts，then return to your vehicle and check if you have “Aux” option under your Audio source menu.(usually at very bottom)

4. Test the AUX Audio

• Go back to your COMAND main menu.

• Select Media → AUX.

• Play music or navigation audio from your CarPlay module.

If you hear sound through the speakers, the activation was successful.

The Result

After enabling AUX Audio, the CarPlay module worked perfectly—crisp audio came through the speakers, and all CarPlay features were fully functional. The customer was thrilled with the upgrade, and we were happy to see another older Mercedes brought into the modern connected world.

Key Takeaways for Mercedes Owners

• If your CarPlay module installs correctly but you have no audio, check whether your factory AUX input is active.

• Many Mercedes-Benz models from around 2010–2014 require AUX activation in Engineering Mode.

• Always handle Engineering Mode settings with care—stick to the AUX activation and avoid changing unrelated options.

✅ If you need help installing a CarPlay module or troubleshooting audio issues on your Mercedes-Benz, feel free to reach out to us. We’re happy to assist or provide step-by-step guidance!