Symphony 2 battery drain (possibly) - help needed


Registered User

Today I tried to get to the bottom of an ongoing battery drain issue with my 2001 S3.

With the car "thinking' it was locked, I used one of these and tested each of the fuses at the end of the dashboard and on top of the battery.

The only fuse reporting any current was fuse 42 (Radio/amplifier).

When the current tester was first connected to fuse 42 the current would peak at 2A while the headunit woke up and loaded CDs etc. After that, the current dropped to 0.0A, but would then jump to 0.3A every couple of seconds. This makes me believe the drain is isolated to fuse 42.

I am now unsure how to troubleshoot the issue further. The headunit is a Symphony 2 and does have a 3.5mm socket connected to the external CD changer connection for external music sources. No other changes have been made to the system.

Despite searching / Googling the forums I could not find any reported issues like this.

I understand the BOSE amps can play up, but not sure how proceed with testing. The sub has been working as normal.

Occasionally I get crackling on front right speaker and the volume control can be slightly erratic. I didn't know if either of these are related to the drain?

For now another new battery has been fitted and fuse 42 has been removed.

Any pointers would be gratefully received.

Many thanks.


Registered User
I am going to disconnect my aux input and see if this is the cause. After that I'd like to isolate the BOSE amp(s) if possible.

Any pearls of wisdom?


Registered User
Hi mate,

Is your stereo coded for 'aux in'?... as I put an 'aux input' in my RNS-E once without coding and it caused the battery to go flat overnight. I think what happens is the 'aux in' keeps 'waking up' the headunit if it hasn't been coded for one...if that makes sense.


P.S. Ignore above information if you're smarter than me...most likely :yes:


Registered User
Thanks @tcg

Nothing has been coded. Can the Symphony 2 be coded?

My aux in is the external CD changer input converted to a 3.5mm socket.

The fluctuations were measured with nothing connected to the socket.