2007 Silverado Classic, 140k, 5.3L Flex Engine
Recently got the engine light with an intermittent message, "Tighten Fuel Cap". I did this a dozen times but still got the message, so I purchased a new fuel cap. I cleared the code but the check engine light came on again, with the same message flashing intermittently.

Is there another part of the system that might be causing this?

Thanks very much,

RickR90s

 

Yep,small evap leak, get your nose down by tank,any fuel odor?could be on top of tank,rusted sending unit?

 

tighten gas cap message would set for a large evap leak.
the evap monitor sees the fuel volume change on start up and knows you put gas it it. It runs a large leak test and does not see a change in the fuel tank pressure sensor when the purge valve is opened and the vent valve is closed.
the most common problem is a stuck/bad canister vent solenoid. post the code and I will walk u thru diagnostics.

 

Thank You tech. I was out of town for a few days so I apologize with the late reply. I'll run my scanner this evening to generate the codes.
Much appreciated.
RickR90s

 

good afternoon, My truck is showing one code.

PO455 EVAP Emission Control System Leak (Large)

I've replaced the fuel cap with no success.

Thank You,

 

does your scan tool have bi-directional control....can you actuate the vent solenoid with your scan tool. if yes, operate the solenoid and listen for the solenoid to click when its opened and closed. if you hear nothing, the vent isn't closing to seal the system during leak testing. diag will start from that point.

 

My scanner is pretty basic. Just reads the codes and allows me to erase them.

I crawled under the truck and near the gas tank, and located the SOLENOID. Fuel Tank Evaporator/Purge Control . The main hose has a plastic connector that was loose, running to the CANISTER. Fuel Tank Evaporator/Purge Control . The hose was original so I replaced that and re-seated the connector. I cleared the error and we'll see if the issue is resolved. I'm guessing that the leak was coming from the loose connection.

Thanks very much for your help.

 

purge solenoid is in the engine compartment, vent solenoid is on the cannister. if the line from the purge to cannister was off...that could have set the code. if the line from the vent to the vent filter was off...its not the problem. Connect it but its not what sets the code.

 

Thanks Tech2, I need to locate those other parts in the engine compartment then. I'm a little unclear what connects to what on this truck.

RickR90s

 

its more likely to be a vent solenoid than a purge solenoid. if the purge wasn't sealing you would a hard start after refueling and possible rich fuel trim dtcs.