TMZ has learned rapper DMX is planning to surrender to authorities in a Los Angeles courtroom and begin serving jail time in connection to a crime he committed "5 or 6 years ago" ... this according to X's manager.

X's manager tells us she's not sure about the nature of the crime -- but insists that DMX is "focused" on taking care of all of his past legal issues so he can move on with his life.

Earlier this month, DMX completed a 4-month jail stint in Arizona ... where he served time for a probation violation.

X's jail stint all stems from a 2002 reckless driving conviction. Turns out, DMX was placed on probation after he plead no contest to the crime ... but has since violated his probation ... and has been ordered to serve 90 days in a city jail facility.