Exhaust Gas Recirculation: Description and Operation

Emission Control Schematic:

DESIGN AND LOCATION
This engine uses two separate EGR systems, one for each cylinder bank.
A single stage EGR valve (89 or 89a) is bolted to the exhaust manifold. The LH control module (N3/2 or N3/3) controls the introduction of exhaust gases via the EGR switchover valve (Y27/2 or Y27/3).

Left EGR Valve (89) And Right EGR Valve (89a):

OPERATION
The switch-over valve is activated (by the LH control module) at coolant temperatures above 65 °C (149 °F) and only if the engine is between the idle and full load condition. When the valve opens, intake manifold vacuum reaches the EGR valve and opens it. Some exhaust gases now flow from the exhaust manifold back into the intake manifold.

NOTE: The left EGR valve (89) mounts to the exhaust manifold at cylinder# 10 and routs the exhaust gases to the intake manifold for the right cylinder bank.
The right EGR valve (89a) mounts to the exhaust manifold at cylinder# 4 and routs the exhaust gases to the intake manifold for the left cylinder bank.