Audi A4 Radio Code — Unlock It Online
If your Audi A4 is displaying SAFE or asking for a code after a battery change or repair, you've landed in the right place. The Audi anti-theft system locks the Concert, Symphony, or MMI head unit every time power is lost — and the only way to unlock it is a four-digit code matched to the unit's serial number. You can get that code online in minutes without an Audi dealer.
Why Does the Audi A4 Radio Lock?
Audi has installed radio immobilisers across every generation of the A4 since the B5 (1994–2001). When the battery is disconnected, discharged, or the fuse is pulled, the head unit registers a loss of power and enters SAFE mode. The display reads SAFE, then — once the ignition is on for up to an hour — it switches to CODE, prompting you to enter your unlock digits. This system makes stolen radios useless without the matching serial-linked code.
Finding the Serial Number on an Audi A4
The serial number format depends on the generation. On B5 and B6 models with a Concert or Classic/Concert unit, the serial begins with the prefix SEZ (manufactured by Philips) and is printed on a label on the unit's body. On B7 and later MMI-equipped cars, Harman-made units also carry an SEZ-format number or an AUZ-prefixed number stored in the MMI menu. Two methods to retrieve it:
- Button combination (B5/B6/B7 Concert): Switch the radio on, then press and hold preset buttons 1 and 4 at the same time for about three seconds. The serial number will scroll across the display.
- Physical label: Use ISO extraction keys to slide the unit partly out of the DIN slot. The serial sticker is on the top or side of the casing.
- MMI menu (B8/B9): On MMI 3G+ cars, navigate to Car → Settings → Version Information via the MMI rotary controller to find the unit's serial.
Once you have the serial, order your Audi A4 radio code here and receive it by e-mail within minutes.
How to Get Your Audi A4 Radio Code
- Retrieve the head unit's full serial number (e.g.
SEZ1Z2A1234567). - Go to the order page on MyRenaultRadioCode.com, enter the serial and your e-mail address.
- Complete secure payment; the four-digit code arrives by e-mail straight away.
- Enter the code using the method for your generation (see below).
How to Enter the Code on an Audi A4
Entry method varies between generations:
- B5 / B6 (Classic / Concert, SEZ serial, Philips OEM): Press preset buttons 1–4 to select each digit. Use the Search/Seek button to confirm the selection and move to the next digit, then press and hold Search to confirm the full code.
- B7 (MMI controller): Use the MMI rotary knob to navigate to the code input screen, dial each digit, and press the knob to confirm.
- B8 / B9 (MMI 3G+): Navigate to Radio → Enter Code using the central MMI controller and touch-pad.
Audi A4 Generations: Radio, Prefix, and Entry Method
| Generation | Years | Head Unit | Serial Prefix | OEM Manufacturer | Entry Method |
|---|---|---|---|---|---|
| A4 B5 | 1994–2001 | Classic / Concert | SEZ | Philips | Buttons 1–4 + Search |
| A4 B6 | 2000–2004 | Concert | SEZ | Philips | Buttons 1–4 + Search |
| A4 B7 | 2004–2008 | Audi MMI | SEZ / AUZ | Harman | MMI controller |
| A4 B8 | 2007–2015 | Audi MMI 3G+ | AUZ / — | Harman | MMI 3G+ controller |
| A4 B9 | 2015–2019 | Audi MMI 3G+ | AUZ / — | Harman | MMI 3G+ controller |
Troubleshooting Audi A4 Radio Errors
- SAFE: Turn the ignition to position II (accessories on). Wait up to 60 minutes. The display will then show CODE, ready for entry.
- CODE: The radio is unlocked and waiting for your four digits. Enter them as described above.
- WAIT / 1000: You have entered the wrong code too many times (typically up to 10 attempts on B6/B7 Concert). Leave the ignition on position II for one hour; the CODE prompt will reappear.
- ERR: The wrong code has been entered. Start the one-hour wait, then re-enter the correct code carefully.
Frequently Asked Questions
How do I find the serial number on an Audi A4 Concert radio?
On B5 and B6 Concert units (Philips OEM, SEZ prefix), hold preset buttons 1 and 4 simultaneously for three seconds while the radio is powered on — the serial will scroll across the display. If this doesn't work, use ISO extraction keys to partially remove the unit and read the label on the casing.
How many wrong attempts can I make before the Audi A4 radio locks permanently?
On B5, B6, and B7 models with a Concert unit, the system allows up to 10 attempts. After each failed batch, a one-hour wait is imposed. There is no permanent lockout on these models — only timed delays. Always double-check the code before entering.
Does the Audi A4 B8 need a radio code?
B8 models with MMI 3G+ (Harman OEM) may or may not require a code depending on specification. Many later B8 and all B9 MMI units are partially vehicle-bound, meaning the code retrieval depends on the specific software version. Our service covers the vast majority of B8 and B9 serials — enter your serial on the order page to confirm compatibility.
My A4 shows SAFE — what does that mean?
SAFE means the radio has detected a power interruption and has locked itself. Turn the ignition to position II and wait up to one hour. The display will then change from SAFE to CODE, at which point you can enter your unlock digits.
Can I get a code for a second-hand Audi Concert radio I've fitted to my car?
Yes. The code is tied to the unit's serial number, not the vehicle. As long as you have the full SEZ or AUZ serial from the sticker or display, you can order the correct code for that specific unit. Order your Audi A4 radio code here.