An electrical secondary air pump which ensures rapid heating of the catalytic converter is used to subsequently treat the exhaust gas during the start phase. During the start phase, the secondary air pump pumps air via the shut-off valve into the manifolds of both rows of cylinders. The two shut-off valves are activated by a pneumatically operated electrical switchover valve. Depending on the engine temperature the valve is operated for a duration of approx. 20 seconds (warm start) up to approx. 100 seconds (cold start). The secondary air pump is also switched off as soon as an engine speed greater than 3000 rpm or full load is reached.