It sounds like you went through a dui court program. Did you agree to do the fourth months as part of your plea agreement. If so, you may try to ask the court to modify your sentence. But it is unlikely since it is a mandatory sentence. The benefit to you is that the allow you to do the time with house arrest instead of in jail.
This is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. This is not intended to be legal advice in your specific case. It's impossible to give detailed, accurate advice based on a few sentences on a website. You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information in your case.
There is usually a reason why the court would impose a punishment of 4 months of house arrest. I assume that you were represented by an attorney to get into the DUI program to avoid jail time. The best solution is to contact your previous attorney and find out why the court is imposing the 4 month house arrest.
120 day sentence is mandatory under the vehicle code. While a court can give credit towards teh 120 days for things like home confinement, and even time at rehab... the rehab needs to have a restriction on liberty however - it needs to be custodial in nature. The Court DUI program is not custodial. Your liberty is not infringed. You're still on the hook for the 120 in some way.
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