A 37-year-old Janesville man is facing a charge of Operating While Intoxicated 4th Offense after being arrested near the downtown.  Janesville police say Christopher A. Dimas was stopped about 1:00 a.m. Friday in the 200 block of North Franklin Street for slow speed and an expired registration.  The officer reports Dimas displayed signs of impairment and failed standardized field sobriety tests.  Other charges include Operating after Revocation and Open Intoxicants by the Driver.