P0401 and P0402 CEL codes

[thesimplyprimshoppe]

I have a 2003 XL7 and keep getting a CEL with the codes P0401 and P0402. They seem to contradict each other. P0401 is Insufficient flow detected and 402 is Excessive flow detected. Does any one have any idea's as to how I should procede?

[SuzukiDon]

Make sure the gas cap is good.
Basic operation of the purge system:
1. Test is started and the computer shuts the vent valve, opens the purge valve and allows vacuum to the fuel tank.
2. Computer shuts off vacuum to the fuel tank by closing the purge valve.
3. Computer then monitors the tank pressure via the tank pressure sensor.
4. If no change or very, very little change then syetm is sealed and all is good.
5. Any change and a flag is set to watch for another failure, 2 fails and on comes the light.
Now, if the gas cap is off or the vent vent is stuck open then the system can't pull a vacuum nor can it see a change in vacuum, thus you set 2 codes.