In the Beam Condition Monitor at the CMS experiment at the LHC, CVD diamonds are used as detectors. During Run 1 operation of the LHC, significant reduction of signal efficiency due to radiation damage was observed. The decrease was significantly stronger than expected. The so-called polarization effect is responsible for this signal reduction. Electric field deformations due to trapped charge carriers are shown in measurements using the transient current technique and compared with simulations.