1. If not as specified, loosen the fuel-filler lid installation bolts, and reposition the fuel-filler lid.
2. Measure the gap and height between the fuel-filler lid and the body.
Clearance
a: 1.7-3.7 mm {0.067-0.145 in} b: -0.5-1.5 mm {-0.019-0.059 in}
3. Tighten the bolts.

Fuel-filler lid and opener removal/installation
BumperMazda 6 Service Manual: Disconnection of the negative battery cable
Before beginning any work, turn the ignition switch to LOCK position,
then disconnect the negative battery cable and wait for more than 1 minute
to allow the backup power supply of the SAS unit to deplete its stored
power. Disconnecting the battery cable will delete the memories of the
...
Mazda 6 Service Manual: No. 1 one or more on-board diagnostic functions inoperative
When performing an asterisked (*) troubleshooting inspection, shake the
wiring harness and connectors while doing the inspection to discover whether
poor contact points are the cause of any intermittent malfunctions. If there
is a problem, check to make sure connectors, terminals and wir ...