Our '05 Tahoe 5.3 has about 58 k miles on it. I have fairly recently had three or four instances in which the check engine light comes on. When I have it checked out at parts shop, they say to tighten the gas cap. I do that, they clear the code and we're on our way. I always tighten the gas cap fully. The last couple times, a message comes on telling me to tighten the gas cap. I've stopped to retighten the cap only to have the check engine light come on. It's on now. Sorry, but I don't know the code. I'll note it tomorrow when I have it cleared again.
What do you think is going on??? Oh - tighten gas cap message the last couple times was after a short rainy section.

Thanks
GaryC - Z71 - Franklin, IN

 

Welcome to the forum,
Try a new gas cap and also make sure you are not over filling the tank, when the pump shuts off the tank is full , don't go for that second try for a few ounces more as it can back up into the evap canister and cause similar but more costly issues.

 

Thanks for the response. I always stop filling when the nozzle shuts off. What is it with gas cap that may influence fault? I turn cap many clicks past tight each time. Do you know if the cap is unique to a Tahoe and to be sourced only at GM or can I try to find one at Auto Zone or Advance?

Take care
GaryC - Z71 - Franklin, IN

 

The fuel system in you vehicle is closed, meaning no pressure or fumes can escape. The vehicle computer checks that pressure and knows if its not with in range and flags a code if its not.
You should be able to find a replacement cap at any auto parts store for about $20

 

Its probably P0440 see below

A code P0440 could mean one or more of the following has happened:

The gas cap is not installed or working properly
The purge solenoid has failed
The canister is plugged and not working properly

Possible Solutions

With a P0440 OBD-II trouble code, diagnosis can be tricky at times. Here are some things to try:

Remove and reinstall the gas cap, clear the code, and drive for a day and see if the codes come back.
Inspect the EVAP system for cuts/holes in tubes/hoses
Inspect for damaged or disconnected hoses around the Evap purge solenoid
Check and/or replace the sensor
Check and/or replace the purge valve

 

Had the codes checked at parts house today. PO 446 and 455. Put a new fuel cap on, but guess I'll have to get a scanner to see if that had any impact.

Take care
GaryC - Franklin, IN

 

Well if the new cap fixes it, then you shouldn't get any more MILs.

P0446 - EVAP Emission Control System Vent Circuit Malf
P0455 - EVAP Emission Control System Leak (Large)

 

We're back on the road after spending a couple hours and $322 at our local Chevy dealer this morning. Evap vent solenoid was defective. It wasn't too bad at $45, but the labor to drop the fuel tank ( 3/4 full) was pretty hefty. Good to go again as we're heading off to NY Sunday.

This was the first money we'd spent on the Tahoe since buying it 10/07. Let's see - spent this $322 or get that '09 Tahoe Hybrid that was on the lot for ONLY $58 thou or so.

Thanks for the help.

Take care
GaryC - Westin grill guard/off road lights/Corsa exhaust(nice rumble)
Franklin, IN

 

I was at the dealer today getting my State Inspection and checked out the 2 Hybrid Tahoe's one black one White both were about $54k

 

Well, 1,464 miles later, we're back from central New York. No further trouble with the check engine light after last week repair. Love our Tahoe on the road. It's just big enough to be a tad intimidating.

Take care
GaryC - '05 Z71 - Franklin, IN