Exhaust Gas Recirculation: Testing and Inspection

Results Of Incorrect Operation
With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:
^ The engine stops after a cold start.
^ The engine stops at idle after deceleration.
^ The vehicle surges during cruise.
^ The vehicle idles roughly.

If the EGR valve stays open all of the time, the engine may not idle. A DTC P0401 may set.

Too little or no EGR flow allows the combustion temperatures to get too high during acceleration and load conditions. This could cause the following conditions:
^ Spark knock (detonation)
^ Engine overheating
^ DTC P0401