here is the service bulletin
GROUP: 14 - Fuel System
DATE: January 21, 2006
Starting with the introduction of 2005 model year vehicles a new diagnostic trouble code (DTC) P0457 - Evap System - Loose Fuel Cap was introduced. Also added to some vehicles was an instrument cluster message in the odometer display or message center (EVIC) that alerts the driver that the gas cap is loose.
The PCM monitors the fuel level for a "significant" change in either direction and remembers that this has recently occurred. A loose fuel cap DTC, cluster message or message center message matures when the check for the EVAP system large leak condition fails after the fuel level change event. If a leak of greater than 0.090" is observed after a fuel level change, a loose cap diagnostic single trip failure is stored and the cluster message or message center message is displayed even though a DTC may not yet be present. DTC P0457 - Evap System - Loose Fuel Cap is stored and the MIL illuminated after 2 cold start failures of the large leak diagnostic checks following a fuel change event. Only the passing of one of the 3 EVAP system diagnostic routines large leak, small leak or loose gas cap) by the PCM will validate that the cap is no longer loose and turn off the MIL light or message.
For 2007 model vehicles DTC P0457 - Evap System - Loose Fuel Cap will be stored and the MIL illuminated after 3 cold starts.
To temporarily clear the gas cap loose message from the odometer or message center press the reset button on the odometer or message center while the message is being displayed. This clears the message for the current key cycle only.
To clear the gas cap loose message from the odometer or message center ensure the gas cap is tight and let the vehicle run the small leak diagnostic routine. The small leak diagnostic routine will pass a sealed system after an 8 hour soak and a negative 3°C change in fuel temperature from the last key cycle.
To clear the gas cap loose message from the odometer or message center and matured DTC (MIL light) diagnose and repair the leak and then erase DTC's with the DRBIII(R)/StarSCAN(TM) scantool
If a gas cap loose message is displayed or DTC P0457 - Evap System - Loose Fuel Cap is set without P0455 - Evap System Large Leak then ensure the gas cap it tight, no further service action is required.
I have a snap on scan tool and when I plug it in it says that there is no codes pending or present. The odometer still keeps flashing gas cap. what do I do next?