The exhaust manifold is a component of the exhaust system used to collect and carry hot exhaust gases away from the engine. Made from cast iron, the exhaust manifold combines the exhaust gases from several cylinders. The exhaust manifold is bolted to the cylinder head with a exhaust manifold gasket between them. The left (front) exhaust manifold connects to a crossover pipe that is part of the right (rear) exhaust manifold and carries the exhaust gases from the front of the vehicle over the transmission to the right (rear) exhaust manifold. The gases are combined in the right (rear) manifold and directed on to the three-way catalytic converter. The three-way catalytic converter pipe and gasket are bolted to the right (rear) exhaust manifold. The right (rear) exhaust manifold has two tapped holes. The heated oxygen sensor (HO2S) threads into the hole by the flange and the EGR valve pipe threads into the hole where the crossover meets the right (rear) exhaust manifold.