If they were not read and you were in custody when the officer questioned then your statements may not be admissible. That does not mean you win your case, only that your statements don't get admitted to the judge or jury. If, for example, you admitted the marijuana was yours and the officer violated Miranda then that admission may not come in. The officer could still testify about the marijuana in the vehicle and the circumstances surrounding the arrest. Good luck.
As you read this response, please bear in mind that this is a public forum on a website, and that this answer does not create an attorney-client relationship, nor is it legal advice; it is simply an answer to a question asked in a public forum. Because it is a public forum, nothing said on this site is confidential or covered by privilege. As with anything in the law, there are exceptions to every rule, and you need to consult an attorney in your area for the best answer. Also, because of regional differences in practice, even within a state, what works in one area may not work in another.
Unfortunately, Miranda means a lot more on TV than it does in real life. The only effect that Miranda has is to determine whether or not your statements (including confessions) can be used against you. It only applies when you are (1) IN CUSTODY, and (2) BEING INTERROGATED BY POLICE. If either of those facts are missing, there is no requirement for the officer to read you your rights.
Here are some prime examples:
a. In custody with no Miranda warnings, but start popping off in the back of the car, unprovoked by the officer--your statements may (WILL) be used against you.
b. Not yet arrested, no Miranda warnings, but being questioned (such as during a traffic stop)--your statements may (WILL) be used against you.
c. Arrested, at the station, no Miranda warnings, and they record your phone call to your buddy when you confess everything--your statements may (WILL) be used against you.
d. Arrested, no formal charges yet, no Miranda warnings, and you brag to a cell mate who is a cop or snitch--your statements may (WILL) be used against you.
A failure to Mirandize a defendant will NEVER, EVER, EVER give the Defendant immunity from the charge or make the case automatically "go away." The best it can do is make a strong piece of evidence (the confession) inadmissible. This usually makes the State's case weaker, which is always good for the defendant. If the confession is the only thing strong enough to connect the defendant to the crime, the case might go away, but that's as good as it gets, and it's EXCEEDINGLY rare.
I agree with both of my collegues. Miranda rights are required when you are in custody and questioned about the facts of the case. Discuss this with your lawyer, as you may be able to suppress the statement. This will not end the case or give you immunity, but it has the potential to affect the strength of ther State's case against you. Good luck.
This response does not constitute legal advice. Given the nature of this website, it does not create an attorney-client relationship. This answer is provided solely for informational purposes, for you to use as a starting point when speaking directly with a lawyer in your State. I urge you to immediately contact an experienced criminal defense lawyer admitted to practice law in your State before you make any decisions about this case.