Exhaust Gas Recirculation Valve  ( EGR )
The exhaust gas recirculation (EGR) system is used to lower oxides
of nitrogen (NOx) emission levels caused by high combustion
temperature. It does this by decreasing combustion temperature.

The main element of the system is the EGR valve. The EGR valve
feeds small amounts of exhaust gas back into the combustion
chamber. With the fuel/air mixture thus diluted, combustion
temperatures are reduced.

If a problem with the EGR system will not allow the PCM to control
pintle position properly, DTC P0404 should set. The PCM also tests
for EGR flow. If incorrect flow is detected, DTC P0401 should set.
See DTC list for other EGR codes.
WARNING LIGHTS