California Attorney Darren T. Kavinoky

Before you're ever pulled over for a DUI offense in California it is a good idea to know what your rights are and what you have already consented to when you were issued your state drivers license.
Under California law, when a driver’s license is issued to you, you have already given your implied consent to submit to a chemical test if you're arrested for driving under the influence whether it be for alcohol, drugs, or a combination of the two. 
Anyone arrested for a first offense of DUI in California only have a short window of opportunity to request a DMV hearing before losing their driving privileges. That time period is 10 days, and if no hearing is requesed, the DMV will automatically begin the process of suspending your driver's license.
Law enforcers can pull you over if they suspect you are driving under the influence or for  something as simple as an equipment violation like a burned out taillight or expired registration.  Bottom line, if you're taken into custody for a DUI in California for a first offense the penalties a stiff and long lasting. 
If you are pulled over the officer is "detaining" you.  What that means is that while you're "not in custody," you're not free to leave.  Because you're "not in custody" the officer does NOT have to read you your Miranda rights before asking some very incriminating questions. Questions like "how much have you been drinking" or "how many drinks have you had." NEVER answer those questions and immediately ask for an attorney or invoke your Fifth Amendment privilege.

In addition to asking you questions about driving under the influence, the officer will ask you to do some field sobriety tests. Again, those are voluntary and they will try to intimidate you into performing them. Will they tell you that, NO.

Keep in mind that most officers in California wear recording devices so it is important to be polite and state that DUI laws in California are too subjective and you would like an attorney.