P0449 again advice please
Thread Starter
Intermediate
Joined: Oct 2021
Posts: 38
Likes: 7
From: Québec, Canada
P0449 again advice please
My car is a 2009 C6 base auto trans.
When I bought the car the GM dealer scan it because the Check engine light was on. He told me I need the Vent valve part number 13575703 and the harness 19257603. So we agree he gave me a discount and I will arrange for the replacement of those parts. I did it but light return 1 hour later. I have read here it's often the gas cap the problem, so I bought a new OEM one and it did not solve the problem, I have a code reader it's always the P0449 code, any help would be appreciated.
When I bought the car the GM dealer scan it because the Check engine light was on. He told me I need the Vent valve part number 13575703 and the harness 19257603. So we agree he gave me a discount and I will arrange for the replacement of those parts. I did it but light return 1 hour later. I have read here it's often the gas cap the problem, so I bought a new OEM one and it did not solve the problem, I have a code reader it's always the P0449 code, any help would be appreciated.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,063
From: Cape Coral, Florida
So are you just looking for what it may be or how to diagnose it yourself ??...the 0449 is a vent valve/control circuit issue so not sure where you saw this could be a bad gas cap ??...the ECM is looking at the voltage on the ground side of the solenoid circuit and if not correct will set the DTC...for a gas cap the ECM is looking at the fuel tank pressure sensor voltage...2 different systems basically....your issue could be no power to the vent valve solenoid, a bad vent valve or the wire that the ECM grounds to activate the solenoid or even a bad ECM...a very easy DTC to diagnose but hopefully the shop that diagnosed it or tried to fix it knew what they were doing !!...find yourself a diagnostic shop.
Last edited by C5 Diag; Oct 31, 2021 at 02:56 PM.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,063
From: Cape Coral, Florida
All you really need to diagnose this yourself is a 12 volt test light and a bi directional scan tool to energize the ground side of your circuit as you may have seen in the video…once the power and ground of the connector are checked and are OK it’s probably a bad vent valve..so you ordered just the pigtail for the connector ??…you can check the new vent valve to make sure it’s good by applying power and ground to the solenoid…it should “click”…just because it’s a new vent valve doesn’t mean it’s good.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,063
From: Cape Coral, Florida
The only thing I can tell you is to check the new vent valve and change it if it is not operating correctly by testing…if you don’t understand how it works you won’t be able to diagnose it correctly…if there is a new valve and harness as you have pointed out best bet is to take it to a “diagnostic” shop and not a repair shop if there is one in your area….changing brakes and oil is one thing but diagnosing cars is a whole different animal !!…good luck my friend !!
Last edited by C5 Diag; Oct 31, 2021 at 06:34 PM.
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Burning Brakes
Joined: Oct 2015
Posts: 820
Likes: 332
From: Orlando Florida
I want to make sure I understand what is going on. You had a P0449 code, replaced the old vent solenoid with a new one P/N 13575703, cleared the code with your scanner, and one hour later the check engine light came on and the reader showed a new code of P0449?
Burning Brakes
Joined: Oct 2015
Posts: 820
Likes: 332
From: Orlando Florida
Thread Starter
Intermediate
Joined: Oct 2021
Posts: 38
Likes: 7
From: Québec, Canada
Today I have checked the new valve and blow in it and put 12 volts on the terminals, everything is ok. Also I have remove the right rear wheel well and blow in the hose of the EVAP canister too, Everything looks ok althought I still have the P0449 code.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,063
From: Cape Coral, Florida
that’s all I can tell you…you may have to bring it to a shop that has that bidirectional scan tool or to a diagnostic shop…they understand how these circuits operate.
Last edited by C5 Diag; Nov 4, 2021 at 09:28 AM.
Thread Starter
Intermediate
Joined: Oct 2021
Posts: 38
Likes: 7
From: Québec, Canada
My local GM dealer told me they cannot check my corvette because their car lifts cannot lift my car, unbelievable but true, I was shocked.
So I will hunt for a garage with bidirectional scan tool.
So I will hunt for a garage with bidirectional scan tool.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,063
From: Cape Coral, Florida
WHAT ????…I don’t believe that !!…then tell them to use a floor jack on the right rear to access the vent valve. If a shop does not have a bi directional scan tool (they should also be using a lab scope) they should close their shop and sell hot dogs from a vending cart.
Last edited by C5 Diag; Nov 4, 2021 at 09:28 AM.
