ECM & Headlight Issues
 

Grandson has a 2011 Mazda 3, gets code P0685 which suggests EMC issues. Previously car stuttered then stopped and would not start. Code read, battery terminals cleaned, tightened, battery charged, talked to dealership and was told a standalone output relay was more likely responsible than the ECM. Relay replaced. Car performed well for about 1/2 a day. Coming home after dark, the car again stuttered, HEADLIGHTS went out, then all was right again after less than 2 seconds. Code read again, P0685 as before. Looking at schematics the only thing I can determine common to both the Headlights and the ECM is the start switch or battery. Headlight could fail due to relay or ECM could fail to cause stuttering, the ignition switch/battery is the only thing in common. With car driving in town, I would not suspect the alternator or the battery as if it was the battery then the car would not have restarted, if the alternator then the battery would not have been charged and car would not have restarted. Previous, extensive failure was in the daylight so unknown if headlights were affected and driving about 10 mph. Have had him start car & bang on the steering column to check for dodgy contact but no joy in mudville. Could be looking at 2 separate problems but I think the odds are quite high for both problems to occur at the same time. Any suggestions? Thanks.