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The P0403 code represents a problem with the Exhaust Gas Recirculation Solenoid or circuit.
Below is the chart that explians and directs us to where the problem may exist.
Since there are a number of components or wires that can be at fault for this code,I feel it is not going to be something that we should attempt to diagnose via long distance. You may wish to check the basic wiring and vacuum supply to the solenoid, but if you find that the ECM is at fault, you will want to have this type of problem backed up by a good part and labor warranty.
Most solenoids need about 20 ohms or slightly higher resistance on the primary winding circuits to function correctly.
Be sure to clear any trouble codes after you have made any repairs to the system.
Below is a technical service bulletin I have located on your vehicle, It may or may not be related to your current problem. I simply wanted you to have it.
TSB Revision: TSB-06-13-012DATE: September, 2006MODEL: See below
SUBJECT:EGR SYSTEM TROUBLESHOOTING- SERVICE MANUAL REVISION
PURPOSEThis bulletin contains additional troubleshooting procedures for the vacuum controlled EGR system on the affected vehicles.
Write the TSB revision number of this bulletin in the "TSB Revision" box at the bottom of the affected service manual pages.
AFFECTED VEHICLES1995-1996 Mirage 1.5L and 1.8L (California emissions only)1996 Mirage 1.5L and 1.8L (Federal emissions only)1997-2002 Mirage 1.5L and 1.8L2003-2006 Lancer 2.0L2003-2006 Lancer Evolution2003 Outlander1996 Galant 2.4L1997-1998 Galant 2.4L (Federal emissions only)1999-2003 Galant 2.4L and 3.0L1995-1999 Eclipse/Eclipse Spyder 420A and 2.0L Turbo1996-1999 Eclipse/Eclipse Spyder 2.4L2000-2005 Eclipse/Eclipse Spyder 2.4L and 3.0L1996-1999 3000GT 3.0L1996 Diamante 3.0L1997-2004 Diamante 3.5L1996 Montero 3.0L 12 valve1996 Montero 3.0L 24 valve (Federal emissions only)1996 Montero 3.5L1997-2000 Montero 3.5L (Federal emissions only)2001-2002 Montero 3.5L1997-1999 Montero Sport 2.4L (Federal emissions only)1997-1998 Montero Sport 3.0L (Federal emissions only)1999-2003 Montero Sport 3.0L1999-2004 Montero Sport 3.5L1996 Truck 2.4L1995 Expo/Expo LRV 1.8L and 2.4L (California emissions only)1996 Expo/Expo LRV 1.8L and 2.4L (Federal emissions only)
The above information is all I have for your Code P0403. I hope this help you determine your course of action.
Have a Great Day
Thanks for the accept and the bonus, Let me look at the P0431.
The P0403 is most likely not related to the P0431, but here's the info I have.
According to my diagnostic charts, there are about 3 possibilities. Catalytic converter, Rear Heated O2 Sensor or PCM failure.