A few weeks ago I got myself a 2004 Trailblazer, 4.2 LT. It drives great but very quickly my CEL came on with the P0455 code (large leak in the EVAP system). I took my car to a local repair shop for a general check up. And because of the P0455 they also did a smoke test but couldn't find any leaks whatsoever. Therefore I simply assumed that the most likely reason for the large vacuum leak must have been a faulty valve in the EVAP system. I took off my vent valve and noticed that it wasn't closing when I tested it with a 12V battery. To save on shipping costs ($42 to the Netherlands ) I ordered the vent valve together with a purge valve and a new gas cap. To make a long story short, I replaced all three items and everytime the CEL came back on. Right now I suspect my fuel tank pressure sensor might be the reason for the P0455 . But before I start orderering parts again I would like to know if there is a way of telling me my FTPS is indeed not working properly. Should there any other symptoms apart from the CEL that I should notice? Any advice would be greatly appreciated!

 

what does the sensor read with the gas cap off. it should be 0 inhg. if its not, disconnect the connector and see if it changes.


install the gas cap. run the engine. with a scan tool, close the vent valve and open the purge valve...you should see a increase in vacuum in the ftp reading.

 

Ok, thanx for your reply!

I only have a simple handheld scanner reading just the basics. Therefore I think I'll bring it to my local repair shop again and ask them to run these tests for me. Hopefully they'll get me back on track...