The engine check light can on last night returning from a cruise in - stopped by the neighborhood Auto Zone to have them scan it - so I replaced the gas cap because I knew it needed replaced but the code came back on going home. I think the tech said it would take several "start-ups" to clear out the code - do you guys agree? What would be my next step tp review the Vapor Canister Purge Valve or ???

 

I had the same problem in my 05, replaced the gas cap with OEM bought off of E-Bay, and drove the car 20 miles, and the light finally went out.

I don't know about starting, cause I started at least three times that day, and the light never went off, but on drive it finally went out and hasn't returned.

 

I'm in the same situation. Light came on 2 days ago. Gotta love the crap gas cap.

 

It won't just be starting and stopping the engine that clears the code. The system needs to test fuel tank pressure, which happens after you drive a bit.

 

Could be a few possible problems.

On the gas cap, you can replace if, or just clean up the old one.
For the most part if it is the cap, it just the sealing ring that needs to be pull, cleaned, given a touch of silicone grease, and will be right as rain.

Next in line, could be the rear solenoid that is the problem.
Its pretty easy to get to pull and test.
To test, with no power on the unit, should be able to suck through it.
Apply 12 volts to the pins on it, should hear is click closed, and should not be able to suck through it instead.
https://www.corvetteforum.com/how-to...ap-code-368173

From here, the joy stops, since we can get into a cracked wire problem in the wiring harness in the front of the torque tube tunnel, or even bad connection in the C186 connector that is tucked on the fender side next to the battery. Or worse, crack in the canister or lines above the fuel tank that the solenoid is controlling or another leak in the fuel tank plumbing instead.

Down and dirty, fuse box sends out 12V positive from the fuse box on the red/white wire hits the solenoid, then has the white return wire that the ECM controls the ground on itself.
So when you start the car, voltage is sent out of the rear solenoid to close it, the front vent solenoid is held closed during the start up test, and the fuel tank pressure sensor is looking for a change in pressure. So since the ECM is monitoring the amount of amperage that the rear solenoid is using, if cracked wire or rear solenoid burnt out, then incorrect amperage use reading back and throws the code. Same with the tank not sealing off so the fuel tank pressure sensor can see the change if pressure as well. So since the system checks itself every start up, if it was just the gas cap the problem that a new gas cap resolved, code will clear itself in about 5 start up checks when each self check comes back as good.

As for how the system works, car off, tank is allowed to vent through the rear charcoal canister above the tank as needed.
Car on, rear solenoid is closed, and the gas tank is percentage vented (vacuum really since it using fuel) from the front vent solenoid via the fuel tank pressure sensor instead. So ECM is looking for amperage use on the system to start with (here we have the electrical part of the math) and then uses the fuel pressure sensor reading to to make sure that the system piping is fine as well.

As for the front vent solenoid, if you have problems with it (t burnt out), will throw a different code, so we can weed that solenoid out as a problem itself.

So gas cap sealer ring that can be pulled and cleaned.
Attachment 48333755

Rear canister solenoid,


And front vent solenoid since I brought it up.

 

Day 2 of the dreaded check light-
Drove 36+ miles to C & C at IMS (yesterday) the light still on - some of the corvette guys had some suggestions: pull the battery cable then reattach may reset the code, another said the code will have to be "erased". I stopped by O'Reilly's on the way home to double check it and still has the P0455 code. So today after ready the comments above (thank you very much) I think I'll replace the rear canister solenoid. Any thoughts about the 2 suggestions mentioned above?

 

I had that last summer. Code would not stay off.

So I had my buddy change the solenoid, problem fixed. It's under the car behind the pass. seat and not all that easy to get out. He has a lift and every tool you can think of.

I'm too old to crawl under the car in the dirt and dick around and I get no satisfaction about fixing things anymore, so the $200 he charged me, part and labor, was well worth it.

 

Mine won't go away.

 

So what have you done to the car so far?

 

Day 3 -
Replaced the rear vapor canister solenoid - started the car - check engine light still on - drove around the block - still on - weather sucks right now so I'll wait until I can drive several miles before blow the car up - LOL - just kiddin,

 

It may not go off by itself, you may have to reset it with a scanner.

Also, there was something about an updated wiring harness that came with the new part. Did you get that?

EDIT: Did you test the old one as Dano laid out above?

 

As stated, before you replace the rear canistor, check it.

My current problem since I have the code as well, is not the canistor, but the white wire from the C186 connector that is broken at the top of the toque tube where the wiring harness goes from soft loom, to hard loom instead. Hence down the torque tube area, the harness has a secondary hard section added to it, but there is a S bend of the wiring harness just before that section that drops down from the top of the fire wire hump area, to the hard section in the tunnel. So as drive train moves around, S section of the harness is moving, and since the White ground wire that leads back to the ECM is so small in gauge.has so few strains to it, it has shaped.

As for testing the harness, Tech II and close the canistor via Tech II for testing. At the rear solinoid connector, should have 12volt positive on the Red/white wire, and white wire should have continuity to ground. In my case, no continuity to ground at the rear connector, so starting probing back on the white wire, and did not find continuity again to ground until just before the harrness drop down the fire wire to the S section. Also, to point out, check from the ECM to C186 connector and had continuity to ground, before and after the connector, to weed out a problem in the C186 connector as well.

I bring this up, since some times the problem is just in the connectors 3 and 4 below that can cause all kind of problems and just need to be cleaned up isntead.


So my joy when the weather gets decent again, car on lift, will need to drop the X pipe, so I can get to the torque tube tunnel plate to remove it as well, then go find the broken white wire in the S section of the cable where it meets the hard added extra piece.

So here is the harness in question, the plug on the left hand side is the C186 connector, and if you follower that cable to where you get to the hard added section of the cable, where my white wire is broken from normal drive line movement. And as stated, to get to that section of wire to fix the crack, you have to pull the torque tube tunnel plate.

 

No did not test the old one - electrical testing is just too "over my head" - I can barely handle a "test light" LOL.

 

Day 3 cont. -
Skies cleared up for a couple hours so I took the car out for a 20 mile run - engine check light is still on - it was mention above that the light may not go out on it's own, that it will need to be "erased" - so how do we know if this is why it's on or if there's still a problem? The parts stores won't clear it and I don't own a scanner so I've got a problem.

 

Question - will disconnecting the battery for 30 minutes clear the code?

 

I'm pretty new to these rolling computers and I do not know the answer to that, but my guess would be no.

The parts stores refused to clear it? Even the one you bought the part from? Seems odd to me.

EDIT: When I had that code on mine last year, I cleared it a few times with my cheap-o scanner but it kept coming back so I knew I had a problem.

 

Day 4 -
Well since the code didn't clear after putting in the rear vapor canister solenoid I decided to take the car to Auto Zone where I bought the parts and have them clear/erase the code (like suggested above). Now I could write 2 pages of the BS I witnessed but I'll spare you all - long story short he couldn't clear the code. So I drove over to a auto shop that has been doing work on all my daily drivers for the last 15 years and he cleared the code - now I didn't drive but about 5 miles after so we still need to cross our fingers - this has been a real learning experience to say the least - about how these cars tick and what you can expect from these auto (joke) parts stores. I wondering if the replaced gas cap would have been the cure alone now, but whatever.

 

If you still have the old part, get someone to help you test it per Dano's write-up. This is something I would absolutely do just to satisfy my mind.

I hate inadvertently "fixing" something and not knowing why. You never learn anything that way.

 

Regarding the auto parts stores. At onetime they would/could clear the codes. I believe it's a liability these days. Can you say attorneys...

 

Buy yourself a scanner and clear it yourself. They are pretty inexpensive and handy to have around.