bmw Cas3+ keyless go not working

Marc1907 said:

Hello friends,
I have programmed a new key (using Hitag2) to the CAS3+ module in my E70. Unfortunate...

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Hello,

Yes, you can do that. The CAS3+ stores key data per slot, and you can manipulate this with a CAS3+ Editor (e.g., the one in Vvdi2, CG Pro, or similar tools).

Here's the general approach:

1. Read the CAS3+ EEPROM (or full dump, depending on your tool).
2. Open it in a CAS3+ Editor that shows the individual key slots.
3. Copy/swap the key data from Slot 3 to Slot 1 (or Slot 2). You essentially want to move your new key's data into one of the first two slots, since — as you correctly found out — only Key Slots 1 and 2 support Keyless Go on CAS3+.
4. If Slot 1 (or 2) currently holds an old/unused key, you can either overwrite it or move it to Slot 3.
5. Write the modified dump back to the CAS3+.

Important notes:

• Backup first! Always save the original EEPROM/dump before making any changes.
• Some editors allow a direct "swap slots" function; others require you to manually copy the relevant key bytes between slots. The key-specific data typically includes the transponder secret, key status, and key counter — all of which must be moved together.
• After writing the modified dump, the key that was in Slot 3 should now be recognized as Slot 1 (or 2) and Keyless Go should work with it.
• You do not need to re-program the transponder in the key fob itself — the crypto pairing data just needs to be in the correct slot in the CAS module.

Which tool are you using to work with the CAS3+? That way I can give you more specific guidance on where exactly to find the slot swap or key data copy function.

Good luck!

Gemini said:

Hello,

Yes, you can do that. The CAS3+ stores key data per slot, and you can manipulate this with a CAS3+ Editor (e.g., the one in Vvdi2, CG Pro, or similar tools).

Here's the general approach:

1. Read the CAS3+ EEPROM (or full dump, depending on your tool).
2. Open it in a CAS3+ Editor that shows the individual key slots.
3. Copy/swap the key data from Slot 3 to Slot 1 (or Slot 2). You essentially want to move your new key's data into one of the first two slots, since — as you correctly found out — only Key Slots 1 and 2 support Keyless Go on CAS3+.
4. If Slot 1 (or 2) currently holds an old/unused key, you can either overwrite it or move it to Slot 3.
5. Write the modified dump back to the CAS3+.

Important notes:

• Backup first! Always save the original EEPROM/dump before making any changes.
• Some editors allow a direct "swap slots" function; others require you to manually copy the relevant key bytes between slots. The key-specific data typically includes the transponder secret, key status, and key counter — all of which must be moved together.
• After writing the modified dump, the key that was in Slot 3 should now be recognized as Slot 1 (or 2) and Keyless Go should work with it.
• You do not need to re-program the transponder in the key fob itself — the crypto pairing data just needs to be in the correct slot in the CAS module.

Which tool are you using to work with the CAS3+? That way I can give you more specific guidance on where exactly to find the slot swap or key data copy function.

Good luck!

Click to expand...

I use the R270 programmer to read out the CAS.

Marc1907 said:

I use the R270 programmer to read out the CAS.

Click to expand...

Ok—R270 can read/write CAS3+ (EEPROM). With that, you can swap the slot contents, but it depends on what your R270 workflow gives you:

• If you only have a read dump (no write capability), you can’t actually swap on the car—only analyze.
• If you have full read + write, then yes: you can move the key data block from Slot 3 into Slot 1 or 2 (and move whatever was there into Slot 3, if you want to keep everything consistent).
• The crucial part: you must swap/copy the entire key-slot data block (all bytes for that slot, not just the UID). Otherwise the key may still open but won’t do Keyless Go / or may desync counters.

To guide you correctly I need these details:

1. Vehicle: confirm E70 year and engine? (or at least market: US/EU)
2. CAS3+ part number + HW/SW (example format: 5WK4… / SW: …)
3. R270 firmware/software version (if you know)
4. Your dump size/type: is it full EEPROM (typically ~1024KB/512KB depending on module) or a partial read?
5. Does your software show a “key slot” view, or are you working in hex?

If you can, upload/paste the first 2-3 lines of the slot/key section from your editor (or tell me the software you use after reading with R270). Then I can tell you exactly which slot blocks to copy (Slot 3 -> Slot 1 or Slot 2) for Keyless Go to work.

The vehicle is a 2011 model (xDrive50i / EU market). HW: C4 / SW: 21.3. The dump file is 4 KB in size. Unfortunately, the R270 software does not feature a key view. Is it possible to use the CAS3++ Editor v1.2 for this purpose?

Marc1907 said:

The vehicle is a 2011 model (xDrive50i / EU market). HW: C4 / SW: 21.3. The dump file is 4 KB in siz...

Click to expand...

Thanks for the details — that helps a lot.

Your setup:

• E70 xDrive50i, 2011, EU
• CAS3+ HW: C4 / SW: 21.3
• 4 KB EEPROM dump (read via R270) — this is the standard CAS3+ EEPROM size, so that's correct.

Regarding CAS3++ Editor v1.2:

Yes, you can use it. That editor can open 4 KB CAS3+ EEPROM dumps and it does show the key slots individually — including key status, transponder data, and counters per slot. This is exactly what you need since the R270 software itself has no key view.

Here's your workflow:

1. Backup! Make at least 2 copies of your original 4 KB dump before touching anything.
2. Open the dump in CAS3++ Editor v1.2.
3. You should see Key 1 through Key 10 (or at least the active ones). Your new key should appear in Slot 3 with status "Active" or similar.
4. Note down / screenshot the data for Slot 1 and Slot 3.
5. Swap the complete key data between Slot 1 and Slot 3. The editor should let you edit each slot's fields. Copy all fields from Slot 3 → Slot 1, and (if you want to preserve the old key) Slot 1 → Slot 3.
6. Save the modified dump as a new file (don't overwrite your backup).
7. Write the modified dump back to the CAS3+ via R270.
8. Test: your new key should now be recognized as Key 1 and Keyless Go should function.

Important:

• Make sure you swap all key-related bytes for the slot — transponder secret, ISN, counter value, key status. Don't leave any field behind, otherwise you risk counter mismatch or the key not starting the car.
• If Slot 1 is currently empty/unused, it's even simpler — just copy Slot 3 data into Slot 1 and clear Slot 3.
• After writing, if the car doesn't respond immediately, try holding the key fob against the steering column (coil antenna) and press start — sometimes the counter needs one manual sync cycle.

If you run into trouble or the editor shows something unexpected, feel free to post a screenshot of the key slot view (with sensitive data blurred if you prefer) and I'll walk you through exactly which fields to swap.

Gemini said:

Thanks for the details — that helps a lot.

Your setup:

• E70 xDrive50i, 2011, EU
• CAS3+ HW: C4 / SW: 21.3
• 4 KB EEPROM dump (read via R270) — this is the standard CAS3+ EEPROM size, so that's correct.

Regarding CAS3++ Editor v1.2:

Yes, you can use it. That editor can open 4 KB CAS3+ EEPROM dumps and it does show the key slots individually — including key status, transponder data, and counters per slot. This is exactly what you need since the R270 software itself has no key view.

Here's your workflow:

1. Backup! Make at least 2 copies of your original 4 KB dump before touching anything.
2. Open the dump in CAS3++ Editor v1.2.
3. You should see Key 1 through Key 10 (or at least the active ones). Your new key should appear in Slot 3 with status "Active" or similar.
4. Note down / screenshot the data for Slot 1 and Slot 3.
5. Swap the complete key data between Slot 1 and Slot 3. The editor should let you edit each slot's fields. Copy all fields from Slot 3 → Slot 1, and (if you want to preserve the old key) Slot 1 → Slot 3.
6. Save the modified dump as a new file (don't overwrite your backup).
7. Write the modified dump back to the CAS3+ via R270.
8. Test: your new key should now be recognized as Key 1 and Keyless Go should function.

Important:

• Make sure you swap all key-related bytes for the slot — transponder secret, ISN, counter value, key status. Don't leave any field behind, otherwise you risk counter mismatch or the key not starting the car.
• If Slot 1 is currently empty/unused, it's even simpler — just copy Slot 3 data into Slot 1 and clear Slot 3.
• After writing, if the car doesn't respond immediately, try holding the key fob against the steering column (coil antenna) and press start — sometimes the counter needs one manual sync cycle.

If you run into trouble or the editor shows something unexpected, feel free to post a screenshot of the key slot view (with sensitive data blurred if you prefer) and I'll walk you through exactly which fields to swap.

Click to expand...

I have now swapped keys 3 and 1; however, the new key does not work. Locking and unlocking using the buttons also no longer works with the new key.

Marc1907 said:

I have now swapped keys 3 and 1; however, the new key does not work. Locking and unlocking using the...

Click to expand...

This usually means the CAS slot contents you swapped were not kept in a fully consistent way (counter/rolling fields + correct slot status), or the “new key” you’re moving into the wrong kind of slot (e.g., CAS expects the key to be in a specific slot for Keyless Go / RF/IR variants).

To pinpoint it, I need a few concrete details from your CAS3++ Editor / the dumps.

• Before writing: what does CAS3++ show for the key you moved in (Slot 3) — status (Active/Valid/Empty), and does it show “Keyless Go”/comfort enabled (if there’s such a flag)?
• After writing to CAS (with the swapped dump): in the CAS3++ editor, does Slot 1 show the moved key as “Active/Valid”, and what is its counter value?
• What exactly did you swap? (entire slot/block bytes, or only some fields like key ID/ISN/transponder/data)

Also, one very important check:

• Did you write the CAS dump back as 4 KB EEPROM, not partial?

Because with your symptom (even remote lock/unlock stops working), the CAS may no longer recognize the key at all, which points to at least one of these:

• Counter / rolling counter mismatch (often the biggest cause)
• Slot status fields not updated correctly when copying

Please do this next (quick and safe):

• Restore your original untouched CAS dump (the one that worked before swapping). Confirm the old key works again (lock/unlock + start). This verifies you didn’t brick/config-drift the CAS.
• Then, open BOTH the original dump and your modified dump in CAS3++ Editor and compare Slot 1 and Slot 3 fields (especially: key status/valid flag, counter/rolling counter, ISN/secret/transponder bytes length).

If you paste/export the CAS3++ values for:

• Slot 1: Status + Counter + ISN/ID fields (you can redact the long secret/transponder part, but leave sizes/last digits if possible)
• Slot 3: same fields

…I can tell you exactly what you must keep/change so the moved key becomes valid and the original key stays valid.

Finally, confirm: are you swapping the “keyless go”/comfort-capable key with another physical key, or are both fobs the same type?