In Order to unlock and E173z-1 you need to follow the below steps carefully which are listed here.
1. Write Down your IMEI Number Somewhere.
2. Generate The Unlock Code and Flash Code using our Huawei Code Calculator http://www.modemunlock.com/huawei-new-algo-unlock-code-calculator.html and note down both at safe place (you have to use NEW ALGO UNLOCK CODE).
3. Now Download E173z-1 (Huawei E173Cs-1) Firmware Update (21.157.13.00.910). http://huaweifirmwares.com /download/e1731-airtel-firmware-download-21-157-13-00-910/
4. Now Connect Your Modem Properly To Computer. http://www.modemunlock.com/connect-modem-properly.html
5. Then You Have To Update The Firmware In To Your Modem (If it ask for the Password Use FLASH CODE as Password).
6. After Successfully Firmware Update You need to Write Unlock Code To Modem http://www.modemunlock.com/write-send-unlock-code-to-huawei-modem.html .
7. Enjoy ….! (Your Modem Is Unlocked Now).
Note :- If you are facing any Issue in Huawei E173z-1 Unlock Find Your Solution Here Huawei E173z-1 Unlocking Problem Solution (E173Cs-1 And E173z-1 Both are Same) http://www.modemunlock.com/airtel-huawei-1731-e173cs-1-problem-solutions.html