VAG Immo5 / MQB — All Keys Lost (AKL) Synch Walkthrough

When a VAG Immo5/MQB vehicle needs an All Keys Lost key made, a new key can't just be written to the cluster on its own — every immobilizer-linked module in the car (engine ECU, gearbox, battery management on E-Trons, etc.) has to be brought into sync with it using its own Component Security (CS) code. HexTool's VAG Immo 5 / MQB – AKL Synch tool takes each module's CS, combines them with the cluster's AES key, and generates the single 32-byte synch token the new key needs. Here's the full process, end to end.

(A video walkthrough of this exact process is linked at the bottom of this post.)

1. Pull the CS from every module in the car

Before opening the AKL Synch tool, you need each module's CS. This example covers a Golf with a DQ250 MQB gearbox and a Simos 18.1 engine ECU.

Gearbox (DQ250): load its EEPROM dump into the ECU Mileage Editor — picking Volkswagen → DQ250 MQB Gearbox as the Vehicle/ECU type reads out the module's PN, VIN, and CS automatically from the dump.

DQ250 gearbox EEPROM loaded, CS extracted, AKL Synch open alongside it

Engine ECU (Simos 18.1): same idea, but picking Simos 18.1 IMMO (VIN / CS / MAC / status) as the ECU type — this reads the ECU's VIN, CS, MAC, and FAZIT string straight out of the flash dump.

Simos 18.1 IMMO editor with VIN/CS/MAC/status decoded

Do this for every module that's actually fitted to the car — the AKL Synch tool only needs a CS for the modules you tick.

2. Open the AKL Synch tool and set the cluster key

Tools → VAG IMMO → Synch File AKL (VAG)… opens VAG Immo 5 / MQB – AKL Synch. Paste the cluster's own AES key into Cluster CS, and set Algorithm to MQB (Immo5 vehicles use the same AES base, MQB adds a wordswap on top — the algorithm dropdown handles that difference for you).

AKL Synch dialog with cluster CS and algorithm set

3. Tick the modules and paste their CS

In Select modules in car, tick each module that's actually present — here, Engine Control Unit – Master and Transmission control unit — and paste the CS you pulled from each one's dump in step 1 into its box.

Leave every module that isn't fitted to the car unticked. Only the modules you tick get included in the generated token, and a module CS pasted into the wrong slot will produce a token the car will reject.

4. Confirm and generate

Pressing Generate shows a confirmation dialog summarizing exactly what you're about to build — the algorithm, the cluster CS, and each module's CS against its name — with a pointed warning:

Make sure each CS is from the correct module. A wrong CS or module cannot be corrected after the key is made — you would have to start over.

Confirm CSes dialog before generating the token

Double-check every value against what you actually read out of each module's dump before pressing Yes — this is the one step in the whole process where a mistake is expensive to undo.

5. Get the token

Once confirmed, the 32-byte token appears in the Output box, ready to copy out and use for the key-making step on your programmer.

Why this matters

Immo5/MQB clusters don't trust a new key based on the cluster alone — every linked module has to agree that the key belongs to this car, and that agreement is exactly what the synch token encodes. Skipping a module, or mixing up which CS belongs to which module, produces a token that looks valid but won't actually authenticate against the real hardware — which is why the confirmation step exists before anything is generated.

Watch it in action

A full video walkthrough of this process:

Watch on YouTube

The AKL Synch generator is part of the VAG IMMO suite in HexTool Full & Ultimate. Full step-by-step docs live in the Help section.

Open the VAG Sync guide

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