Problem: The vehicle came in for a leak from the
fuel tank area.
The technician found the fuel tank had collapsed and the seams
were beginning to split. Strangely, there was no MIL on or DTCs
from any modules. Early testing revealed that the EVAP system had
no restrictions. Acting on the advice of the Tech-Assist
consultant, he used a scan tool to command the canister purge and
vent valve solenoids to operate. If either one was sticking open
or closed, the gas tank could be subject to engine vacuum.
On test drive with the scan tool still connected, the tech
noticed the fuel tank pressure sensor PID indicated very high
vacuum. The canister purge and vent valve solenoids were
operating properly so the technician checked the EVAP canister.
He found the canister was restricted causing engine vacuum to be
applied to the fuel tank.
Confirmed Repair: The EVAP canister and the
gas tank was replaced, then the truck was taken on a long test
drive. The fuel tank pressure sensor PID was within factory
specifications and the tank showed no signs of collapsing.