Date: 201508
Local time of day: 1201-1800
Location: OAK.Airport, CA
Flight conditions: IMC
Weather elements / visibility: 5
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class E NCT
ATC / advisory: TRACON NCT
Aircraft component: Approach Coupler
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: We were flying the RNAV Arrival into Oakland and were cleared for the approach to 30L. It was about a 45 degree intercept to the 296 course from the arrival. The FO selected approach mode prior to the Localizer. Upon reaching the Localizer course; the aircraft did not join the course (autopilot on) and instead; continued in a right turn. By the time we corrected; the aircraft was about 30 degrees off course. Approach queried our deviation and gave us a heading to rejoin the Localizer.


Second narrative: We were on the EMZOH1 Arrival and cleared the ILS Runway 30 approach. Aircraft autopilot coupled to my side (CMD B); displaying LNAV and VNAV. Aircraft was following the proper course and altitude.Enroute to [MYCAF]; VOR/LOC was selected. After VOR/LOC capture; APP was selected. Aircraft displayed G/S and started descending. I immediately noticed I did not have any glideslope indications on my ADI. By the time I verbalized this to the Captain; the aircraft immediately rolled into a right 30 degree bank turn; away from the LOC course. I intervened with CWS R and CWS P and rolled back left towards the course. I verbalized what was happening; and stated I did not have good information.Approach Control queried us about the deviation; and gave us a vector for the ILS. During the time I did not have good ILS information; I verbalized that we were safely above the minimum approach altitudes and I passed aircraft control to the Captain. We broke out of the weather shortly after we transferred control. The aircraft was maneuvered visually and configured for a safe landing.The Captain and I were not clear why the aircraft veered off course. I informed the oncoming Captain of the LOC/glideslope issue; and recommended they pay extra attention during their ILS approach. Continually monitor 'Source Annunciation' display on the upper left of ADI; and be aware that the aircraft can aggressively roll away from course if there is a navigation issue.


Synopsis: B737 flight crew reported an autopilot anomaly while attempting to intercept the LOC and glideslope with the approach mode armed. Upon LOC intercept the autopilot turned right as if to join but continues in the right turn away from the LOC before the First Officer intervenes. ATC takes note of the deviation.