No, automatic renewal does not guarantee the continuation of the same old return.
Key points
At maturity, the certificate may be renewed at the price and terms of the product then in effect, or to an alternative product according to the bank's rules.
A few days before maturity, contact the bank to find out the current renewal rate and decide whether to let it renew or switch to a better product.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.