Car Stereos: No Sound, Jeep GC 2006, rear cargo area, grand cherokee

Question
Hi, just installed a replacement DDIN head unit in my 2006 Jeep GC, i had power but no sound, realised that if i reconnected the factory head unit, turned up the volume and then disconnected and plugged in the new unit then I had sound but once i turn off ignition and turn on again, the sound has gone. Please can you help me its been driving me mad!!!!

Answer
Hi Andy,

I'm really only familiar with the Grand Cherokee sold in the North American market.  Hopefully the UK version is similar enough that this answer will be useful.

It really sounds like your vehicle's audio system includes a data-controlled factory amplifier.  This is a relatively recent development in OEM car audio systems, but many manufacturers are using this type of setup--especially in the optional "premium" audio packages.  In this case, the speakers are driven by an amplifier, located under the trim panel on the left side of the rear cargo area.  The factory head unit and amplifier are connected through the vehicle's data bus system.  The head unit sends a 2-channel, fixed-level audio signal to the amplifier.  When you adjust the head unit's volume, or the balance and fader controls, you're not changing the level of the head unit's output.  Instead, you're sending data commands from the head unit to the amplifier, so that the amplifier changes the level of the amplified signal sent to the speakers.

The trouble is, an after-market head unit isn't capable of producing the data commands that the factory amplifier requires.  In fact, it can't even tell the factory amplifier to turn on.  That's why the system only works after the amplifier has been switched on by the factory head unit; and the next time you turn the car off, the amp switches off and will need new data commands to turn it back on again.

You have two options:

First of all, you can purchase an adapter interface that will let your new head unit work with the factory amplifier.  These devices tend to be expensive.  An example is the CHTO-01 made by Metra Electronics.  Other manufacturers, such as PAC Audio and Precision Interface Electronics, make their own versions.  Some models allow you to use the new head unit's fader control, and some do not.  I'm not sure which interface adapters are available in your area.

The second option is to bypass the factory amplifier, and re-wire the system so that the speakers are connected directly to the new head unit.  Usually, I don't recommend this unless you're planning to replace the stock speakers with after-market upgrades.  Because an after-market head unit typically only has outputs for four speakers, you might need to give up the dash tweeters if you choose to bypass the amp.

Hope this helps!

Brian