Exhaust Gas Recirculation: Testing and Inspection

Diagnosis

The EGR system is monitored by the PCM in order to detect when a failure occurs that causes emission levels to rise more than one and one-half times normal levels. If the PCM detects that the a system failure has occurred due to a restriction, a DTC P0401 will be set. If the PCM detects that it cannot control the EGR valve as it has commanded, a DTC P1406 is set. Exhaust Gas Recirculation (EGR) System Diagnostic will check normal operation of the EGR system. Refer to the applicable table for diagnosis.


Results of Incorrect EGR System Operation

Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:

^ Engine stalls after cold start.

^ Engine stalls at idle after deceleration.

^ Vehicle surges during cruise.

^ Rough idle.

^ DTC P0300.

^ DTC P1406.

Too little or no EGR flow may allow combustion temperatures to get too high. This could cause:

^ Spark knock (detonation).

^ Engine overheating.

^ Emission test failure.

^ DTC P0401 or DTC P1406. Poor fuel economy.