FAQ
TL;DR: On A4 B7, rear speakers/sub stay silent if you mix ISO (B6) with ISO2 (B7); Symphony II+ has a "built-in changer for 6 discs." [Elektroda, Sas_AS, post #16846987]
Why it matters: This FAQ helps Audi A4 B7 owners restore full factory audio—rear channels, sub, antenna, and controls—without chasing the wrong parts.
Quick-Facts
- B7 typically uses ISO2/Fakra with dual antenna inputs; older ISO radios leave only fronts playing. [Elektroda, Sas_AS, post #16795534]
- Weak FM can come from the wrong antenna adapter ("balun") or a damaged Fakra pin. [Elektroda, Sas_AS, post #16790515]
- Symphony II+ replaces the cassette with a 6‑disc internal changer (no glovebox changer needed). [Elektroda, Sas_AS, post #16846987]
- A full Fakra→ISO2 harness plus antenna reducer is the correct adapter set. [Elektroda, SZYMON BYDGOSZCZ, post #16796706]
- Using the proper ISO2 head unit (Concert II+/III or Symphony II+) is the cleanest fix. [Elektroda, Sas_AS, post #16795534]
Quick Facts
- B7 typically uses ISO2/Fakra with dual antenna inputs; older ISO radios leave only fronts playing. [Elektroda, Sas_AS, post #16795534]
- Weak FM can come from the wrong antenna adapter ("balun") or a damaged Fakra pin. [Elektroda, Sas_AS, post #16790515]
- Symphony II+ replaces the cassette with a 6‑disc internal changer (no glovebox changer needed). [Elektroda, Sas_AS, post #16846987]
- A full Fakra→ISO2 harness plus antenna reducer is the correct adapter set. [Elektroda, SZYMON BYDGOSZCZ, post #16796706]
- Using the proper ISO2 head unit (Concert II+/III or Symphony II+) is the cleanest fix. [Elektroda, Sas_AS, post #16795534]
How do I get my rear speakers and subwoofer working again on an A4 B7?
Use a full ISO2 adapter between car and radio. It carries the rear amp/sub signals. With the proper harness, the active sub and rear speakers start playing. If you keep the current ISO radio, expect limited function without rewiring. "Adapter between those marked in red" solved it for the thread author. [Elektroda, Sas_AS, post #16796765]
Which factory radio actually belongs in a 2006 A4 B7?
B7 favors ISO2 units like Concert II+/III or Symphony II+. Verify via equipment codes or VIN. If your car has glovebox changer wiring, Symphony II+ is less likely, because it has an internal 6‑disc. Check rear-left arch for additional modules, too. [Elektroda, Sas_AS, post #16795534]
How can I tell if my harness is ISO2/Fakra?
Look for a dual Fakra antenna plug and multi-block connectors behind the radio. That layout points to ISO2-era Concert III/Symphony II+. If only the front speakers work with your current unit, you likely mismatched ISO vs ISO2. [Elektroda, Sas_AS, post #16795534]
Do I need an adapter if I insist on keeping an older ISO Symphony II?
Yes. Search for an Audi ISO↔ISO2 adapter and an antenna reducer. Plan extra pin-out tweaks for features like changer or controls. It’s quicker to fit the right ISO2 radio than to rework the loom. [Elektroda, Sas_AS, post #16875028]
Will a partial adapter fix it?
No. A partial loom leaves rear audio dead. You need the full adapter that fills the blue and green cavities and converts to the three-piece yellow/blue/green block. Even then, some functions may still need modification. [Elektroda, Sas_AS, post #16875190]
My FM reception is weak—what should I check?
Inspect the antenna path first. The wrong "balun" adapter can overdrive the tuner. Also check for a broken center pin in the Fakra plug and verify the diversity antenna feed. Replace the adapter with a correct Fakra unit. [Elektroda, Sas_AS, post #16790515]
Will the glovebox CD changer work with Symphony II+?
No. Symphony II+ includes a 6‑disc internal changer, so the glovebox changer is typically absent or unused. Seeing a glovebox changer suggests a different head unit originally, like Concert with external changer support. [Elektroda, Sas_AS, post #16846987]
What’s the easiest factory-correct solution overall?
Install an ISO2-native head unit that matches your harness (Concert II+/III or Symphony II+). This avoids splicing, restores rear channels, and supports factory modules. It’s the recommended path from experienced installers in the thread. [Elektroda, Sas_AS, post #16795534]
How can I confirm what my car had from the factory if the trunk sticker is missing?
Check equipment codes in the service book, or ask by VIN. Also inspect the rear-left wheel arch compartment for modules (changer, TV, DAB). Their presence hints at the original radio type. [Elektroda, Sas_AS, post #16795534]
What is the CAN bus and why does it matter for the radio?
CAN bus is the car’s data network that carries control signals. B7 uses CAN-integrated radios; mismatched radios or adapters can break features like controls or power management. Use an ISO2/CAN-correct unit or a proper interface. [Elektroda, Sas_AS, post #16790515]
Will steering-wheel controls and FIS still work if I change radios?
They can, when the radio matches the car’s CAN and ISO2 wiring. One B7 1.9 TDI owner reports all speakers, sub, and FIS info working on their Symphony setup. Results vary with electronics version. [Elektroda, henryxxl, post #16824033]
Could my current radio be from a B6? Does that matter?
Yes. If only the fronts play and connectors don’t match, you’re likely running a B6-era ISO unit. In a B7 ISO2 car, that’s the wrong match. Fit the proper ISO2 radio or use the full adapter set. [Elektroda, Strumien swiadomosci swia, post #16793409]
Quick how-to: restore factory audio on an A4 B7
- Inspect behind the radio for dual Fakra and ISO2 blocks.
- Source a Concert II+/III or Symphony II+ head unit.
- Install a full Fakra→ISO2 adapter and antenna reducer; test rears and sub.
“Change the radio to the right one” if issues persist. [Elektroda, Sas_AS, post #16875028]