On the 2006 Pontiac Torrent, the P0455 is “EVAP System Large Leak Detected”. This is a very “general” code, and there is no 1-answer, “it’s this…” kind of answer. There will need to be some testing done. If you have already replaced the Fuel Cap, make sure the replacement cap meets Pontiac OE specs. Most after market caps (like from Auto Zone) do not meet specs. Locking or Universal caps also do not meet specs. If you are certain the Fuel Cap is good and sealing correctly, then the next best course of action is to have the EVAP system “smoked”. This is where a machine forces smoke through the EVAP system and the leak will reveal itself with a stream of smoke. Once the smoke test proves no leaks, then the EVAP Purge Solenoid and Fuel Tank Pressure Sensor will need to be tested for proper operation (requires the use of a scan-tool).
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