German car manufacturer Mercedes-Benz has made a weaker start to the year than expected due to problems in the supply chain and model changes. Turnover in the first quarter fell by 4.4% to €35.9 billion ($37.4 billion), the Stuttgart-based company announced on Tuesday. Earnings before interest and taxes even fell by almost 30% to €3.86 billion euros. Passenger cars, the company’s most important division, saw its operating profit margin before interest and taxes adjusted for special effects slip sharply by 5.8 percentage points to 9.0%. The management around CEO Ola Källenius had already warned…