BMW 18407556504 Exchange Exhaust Manifold With Catalyst

To remove the exhaust manifolds on a 3.0L engine: Raise the front of the vehicle and remove the engine splash shield. Remove the nuts securing the manifold outlets to the exhaust system. Disconnect the electrical connectors for the oxygen sensors. Remove the cover over the ignition coils and the coolant expansion tank. Remove the rear and front exhaust manifolds, taking care not to damage the oxygen sensors. Discard the gaskets.

The performance of the catalytic converter is monitored by the oxygen sensors. When a change in readings occurs between the upstream and downstream sensors, a trouble code is set, indicating that the catalytic converter is not working efficiently.