This bulletin applies to 2017 BMW vehicles equipped with the B58 engine. A rattling noise may be heard from the rear exhaust flap during initial start-up. The rattle may last up to 60 seconds.
The cause may be a DME software application error which may cause the flap to stay in an undefined position which will cause it to rattle. Or, this may be caused by a loose or failed bow (clip that connects the exhaust flap actuator to the flap). Or there may be excessive play in the pivot bushing of the exhaust flap.
Check the exhaust flap on cold start. The flap should remain closed for 30-60 seconds for catalyst warm-up. If the flap does not fully close during this warm-up, reprogram the DME to F020-17-11-540 or higher.
If the fixing bow is loose or damaged or missing, replace the fixing bow. If the flap is operating as designed, apply pressure to the bushing of the flap. If the rattle goes away, replace the rear muffler with exhaust flap.
