BMW fault: 4873 Exhaust gas recirculation cooling, plausibility - fault is due to an error in monitoring EGR cooler bypass flap.
1. Check the vacuum supply to the exhaust gas recirculation cooler bypass flap (vacuum lines and changeover valve).

2. If the vacuum supply is OK:

Replace the exhaust gas recirculation cooler (throttle return spring of bypass flap may be faulty).