Well I don't believe it for one second. The mechanic must have disconnected the fuel pressure sensor or maybe just accidently pulled it out of it's seating position. Fixing one code does not cause an other code to pop up.
The fuel tank pressure (FTP) sensor measures air pressure or vacuum in the evaporative emission (EVAP) system. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal voltage varies depending on EVAP system pressure or vacuum. This DTC will set if the control module detects an intermittent signal from the FTP that would prevent the engine-off small leak test, DTC P0442, from running.
This diagnostic procedure supports the following DTC:
DTC P0454 Fuel Tank Pressure (FTP) Sensor Circuit Intermittent
Conditions for Running the DTC
• DTC P0454 runs only when the engine-off natural vacuum small leak test, P0442, executes.
• This test can run once per engine-off period. The length of the test can be up to 10 minutes.
• A refueling event is not detected.
Conditions for Setting the DTC
If, during the engine-off natural vacuum small leak test, P0442, the engine control module (ECM) detects an abrupt FTP signal change, other than a refueling event, this DTC will set. An abrupt change is defined as a change of 1 inch H2O in the span of 1 second.
Just push on the fuel pressure sensor to make sure it is in all the way. It is just press fit in place and sits just below the EVAP valve solenoid. This is what it looks like.
And this is where it hides....