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Hey guys,

So twice now I've had both P0455 and P0442 codes appear, and I once got the 'tighten gas cap' message on the DIC. It looks to me like the car has an aftermarket gas cap (which never hisses when I open it), so that will be the first thing I check but I wanted to run it past you guys as well.

The other issue I've been noticing since I bought this car recently is the terrible terrible gas mileage I'm getting. I drive 100% city miles, and whether I'm driving gently or harshly, I've consistently been getting around 19-20 L/100km (11-12 mpg) which is way worse than my previous car (a 2005 V6 Camry, I was expecting similar mileage as it's a similar car).

So my first step will be the gas cap, if not that then I'll take a look at the gas filler tube (which apparently can rot, or rust from road salt), then the solenoid vent valve.

Just wanted to double check if there's anything I'm missing, or if you guys can diagnose something else based on the gas mileage symptom I'm also experiencing. I'm also from a country that doesn't experience winter like Canada does, so I've heard mentions of 'winter blend gas' but I don't know what that is or how it affectes gas mileage

Thanks
 

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'12/'13/'16 Limited LT's
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3,699 Posts
Hey guys,

So twice now I've had both P0455 and P0442 codes appear, and I once got the 'tighten gas cap' message on the DIC. It looks to me like the car has an aftermarket gas cap (which never hisses when I open it), so that will be the first thing I check but I wanted to run it past you guys as well.

The other issue I've been noticing since I bought this car recently is the terrible terrible gas mileage I'm getting. I drive 100% city miles, and whether I'm driving gently or harshly, I've consistently been getting around 19-20 L/100km (11-12 mpg) which is way worse than my previous car (a 2005 V6 Camry, I was expecting similar mileage as it's a similar car).

So my first step will be the gas cap, if not that then I'll take a look at the gas filler tube (which apparently can rot, or rust from road salt), then the solenoid vent valve.

Just wanted to double check if there's anything I'm missing, or if you guys can diagnose something else based on the gas mileage symptom I'm also experiencing. I'm also from a country that doesn't experience winter like Canada does, so I've heard mentions of 'winter blend gas' but I don't know what that is or how it affectes gas mileage

Thanks
Model year/engine?
 

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2009 Impala SS
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1,827 Posts
Filler caps rarely fix evap leaks.
You aren't in the salt and snow where you would have issues rotting out the filler neck.

You need to diagnose this instead of loading the parts canon and saying a Hail Mary.

A 168 peanut bulb with Male Metripak 150 terminals and a bi-directional diag tool is needed. A vacuum gauge can be used but isn't strictly neccesary.

Plug your diag tool into the J1962 diag jack, turn the key on but don't start the engine, then go to the EVAP diagnostic menu.

Command the EVAP vent closed and listen near the fuel filler. You should hear the vent valve click when you command it to change state.
Test with a 168 peanut bulb. The bulb should light when the vent valve is commanded closed. This proves the electric circuit is working.

Start the engine.
Remove the EVAP hose and the electrical plug.
1- Vacuum with the purge valve plug removed means the valve is worn out.
2- Plug the valve back in and command the purge valve to 50% duty cycle. No vacuum with the valve commanded open means the valve is failed or the electrical to the valve is damaged. Test with a 168 peanut bulb. The bulb should light when the purge is commanded open. If it lights and the valve isn't opening to make a vacuum then the purge valve is failed.

If the purge valve is working set the vent closed and the purge to 40% duty cycle. Watch the tank pressure for a pressure drop. If the tank pressure doesn't change and you don't hear the suction from a leak at the Left Rear corner the fuel tank pressure sensor is suspect.
 

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2014 Chevrolet Impala LTZ 3.6
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10 Posts
Filler caps rarely fix evap leaks.
You aren't in the salt and snow where you would have issues rotting out the filler neck.

You need to diagnose this instead of loading the parts canon and saying a Hail Mary.

A 168 peanut bulb with Male Metripak 150 terminals and a bi-directional diag tool is needed. A vacuum gauge can be used but isn't strictly neccesary.

Plug your diag tool into the J1962 diag jack, turn the key on but don't start the engine, then go to the EVAP diagnostic menu.

Command the EVAP vent closed and listen near the fuel filler. You should hear the vent valve click when you command it to change state.
Test with a 168 peanut bulb. The bulb should light when the vent valve is commanded closed. This proves the electric circuit is working.

Start the engine.
Remove the EVAP hose and the electrical plug.
1- Vacuum with the purge valve plug removed means the valve is worn out.
2- Plug the valve back in and command the purge valve to 50% duty cycle. No vacuum with the valve commanded open means the valve is failed or the electrical to the valve is damaged. Test with a 168 peanut bulb. The bulb should light when the purge is commanded open. If it lights and the valve isn't opening to make a vacuum then the purge valve is failed.

If the purge valve is working set the vent closed and the purge to 40% duty cycle. Watch the tank pressure for a pressure drop. If the tank pressure doesn't change and you don't hear the suction from a leak at the Left Rear corner the fuel tank pressure sensor is suspect.
I'd give this one another like if I could.
 

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2009 Impala SS
Joined
1,827 Posts
I'd give this one another like if I could.
GM EVAP diagnosis is super easy.

You haven't lived til you've diagnosed the overcomplex Toyota EVAP systems. LOL

I failed to mention why I recommended using a #168 peanut bulb to test the EVAP Vent & Purge valve control instead of a multimeter. A multimeter doesn't have enough resistance to prevent the power to the EVAP valves from burning out the ECM control circuits. GM switches the ground and provides ignition switched power to the EVAP valves. Personally GM should've hardened the control circuits but it would've added $0.05 to the cost. A Power Probe III & IV can test the control grounds without damaging the ECM but they're pricey little buggers for occasional use. The Power Probe III is around $100 and the Power Probe IV is around $180. I worked on public transit rubber tire & rail electronics and electrical before retiring. I still do a lot of automotive, trailer, and machinery electrical work along with Light, Medium, & Heavy trucks so I keep buying toys.
 
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