Arrange a free consultation with one of the AVVO lawyers in the San Jose area. Discuss the situation with them and if you can, hire one you feel comfortable with. They can then deal with the warrant and arrange for you to turn yourself in. And before you turn yourself in, talk to a bail bondsman and get a bail set up so if a bail is set, you can bail our right away. Since you got a letter, sounds like it might be a misdemeanor charge.
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You should hire an attorney immediately. These are serious charges. You likely missed a court date after being arrested or cited for the criminal offense you're charged with. An attorney can put your matter on calendar and keep you out of custody during the duration if the case. A bondsman should be consulted if you are put in custody so you can post bail and be released. Good luck.
I disagree with the comment that you "likely missed a court date". You stated this was an arrest warrant, not a bench warrant. SJPD routinely sends out arrest warrants by mail and gives you an opportunity to take care of the warrant on your own. I don't know how anyone can question whether you need a lawyer or not. Of course you do. You are charged with False Imprisonment. Although you don't mention if the arrest warrant had an "F" next to it or the bail amount so I don't know if it's a Felony or Misdemeanor false imprisonment charge. 236/237 is a "wobbler" meaning it can be charged both ways. The best advice is to get a lawyer. They can direct you to a reputable bail bondsmen. If you can't afford a lawyer then contact the Public Defender's office. This is not something you can handle via a chat room or internet forum. Find a local lawyer you feel comfortable with.