Possible Causes

WARNING: This page is about a different car, the 2003 Mazda B4000, 2003 Mazda B3000, and 2003 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

Possible causes are:

Carbon buildup in EEGR valve seat (DTCs P0400 or P1408).
Connector to EEGR not seated (DTCs P0400, P0403 or P0408).
Damaged PCM (DTCs P0400, P0403 or P1408).
EEGR motor windings shorted or open (DTCs P0400, P0403 or P1408).
EEGR valve stuck open or closed (DTCs P0400 or P1408).
Harness open or shorted to power or ground (DTCs P0400 or P1408).
MAF/IAT sensor signal erroneous (DTCs P0400 or P1408).
No power to EEGR (DTCs P0400 or P1408).
One or more sensors not responding or out of range (DTCs P0400 or P1408).
Open or short in harness from PCM to EEGR (DTC P0403).
Short circuit in EEGR motor (DTC P0403).
Vacuum signal to MAP restricted or leaking (DTCs P0400 or P1408).