Hi and welcome to Just Answer.I will try and assist you today with your question.Please don't click on accept unless you feel satisfied with my assistance here.
I just need a little more info to assist better.
Was the EVAP system tested or smoke tested at all or was an EVAP test done at all with a scan tool?
Let me know so we can continue,thanks Pete!
What model and engine size is this vehicle?
Our mechanic has used a GM Tech 2 tool - the code is not failing for emissions, but that there is a malfunction in the system
O.k.,what needs to be done is what is called an EVAP test,this is done with a scan tool itself and the vehicles computer is put into test mode and runs the evap components to see what is causing this issue.Then if found it is a leak then a smoke test should be done,this is done by injecting smoke into the fuel system and closing the vent valve operation with a scan tool,then where the smoke leaks out is the source of the leak that needs repaired.If you can tell me the model of this vehicle I can further check for more info that may be specific to this vehicle here.
2002 Chev Cavalier -2.2OHV engine - VIN 1g1jc124827236562
The diagnoistic equipment the mechanic uses - he said should diagnose any leaks. He has done the above mentioned repairs, turns the light off then the next day or so the light comes back on.
O.k.,this indicates the computer isnt seeing the vacuum it wants to see in the evap emissions or fuel tank.He needs to test to make sure the purge solenoid is coming on when it should and that when it does come on there is vacuum present from it,then if this is o.k. he needs to make sure the hose/pipe that leads from the purge solenoid isnt damaged where it runs to the canister as well as no other leaks in the system.If all of these chekc out o.k. then this can be caused by a faulty fuel tank pressure sensor as this is the sensor that sends the vacuum readings to the computer and if it is reading wrong due to an electrical fault with it then this code will set,from what has been tested and replaced here this sounds like the component that may be at fault needing replaced.
It is either located on top of the fuel tank with an electrical connection plugged into it or on top of the fuel pump assembly and can be removed from the top of the fuel pump assembly and replaced seperately.
Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!