My 2004 Tahoe threw a P0442 code

[ueww40]

My 2004 Tahoe threw a P0442 code the other day. 5.3 ltr flex engine. I understand it is a small leak somewhere in the evap system. I visually inspected all the lines to see if I could find something broken, but they all seem to be in order. I don't think it is the gas cap. The cap and seals look good and it feels right when I turn it the way it always has and should. How do you check the vapor canister vent valve and the vapor canister purge valve for proper operation? Should they be open or closed in home position? I inspected the vent valve to see if it was plugged up with dust or dirt, but it was not. Any ideas from experience what it could be? All suggestions are welcomed and appreciated.

 

[Scottydoggs]

smoke test will help a ton.

the evap line does go all the way up to the engine, so look for a broken line up there as well.

 

[Big Mama]

Just chased this on my 07. I started with the cheap fix a new gas cap. My problem was vent valve solenoid on top of engine. A decent scanner or a tech2 can really narrow it.

 

[ueww40]

This problem has not been resolved yet. I was just away for a while. Here is what i did so far. I had my son, who vapes, blow a lot of smoke thru the AVAP service port right next to the Vapor Canister PURGE valve (the one with the green cap on and the left threaded Schraeder valve in it (for crying out loud why is the thing left threaded. I almost busted the whole thing trying to get it out until I figured out that it was a lefty.)), but that did not show any leaks. I figured, he may not be blowing hard enough so I actually went and ordered a smoke making machine, which worked like a charm, but there were NO leaks to be found anywhere. The only place where smoke came out was at the end of the line at the Vapor Canister VENT valve. I understand that the PURGE valve is normally closed (engine not running) and the VENT valve is normally open (engine not running). Can anybody explain to me what the function is of these 2 valves and how they are supposed to be doing whatever it is they are supposed to be doing while driving. Is there anything else that could cause a code P0442?

 

[ueww40]

Just chased this on my 07. I started with the cheap fix a new gas cap. My problem was vent valve solenoid on top of engine. A decent scanner or a tech2 can really narrow it.

I thought the valve on top of the engine was the PURGE valve and the VENT valve is under the car. Please correct me if i am wrong.

 

[swathdiver]

My 2004 Tahoe threw a P0442 code the other day. 5.3 ltr flex engine. I understand it is a small leak somewhere in the evap system. I visually inspected all the lines to see if I could find something broken, but they all seem to be in order. I don't think it is the gas cap. The cap and seals look good and it feels right when I turn it the way it always has and should. How do you check the vapor canister vent valve and the vapor canister purge valve for proper operation? Should they be open or closed in home position? I inspected the vent valve to see if it was plugged up with dust or dirt, but it was not. Any ideas from experience what it could be? All suggestions are welcomed and appreciated.

This can be hard to trace. A bi-directional scan tool can put vacuum in the system and test the vent and purge valves to eliminate them. I've done this with mine and they passed. There are also lines above the fuel tank that can leak as can the Fuel Tank Pressure Sensor. The last time mine threw the P0442, it threw one for this sensor too. I cleared them and kept driving. Gas cap being a little over two years old with my children and wife fueling the truck, I just now put a new ACDelco cap on for $16 as I don't want to spend the money on a smoke machine yet. The code shows up usually every 16 or 18 ignition cycles but we're now at 21 or so and haven't seen it yet.

This code usually throws during over night when the computer runs the tests.

It's a colossal waste of time, money and resources to make the do-gooders feel good. Someday I'll throw all this stuff in the garbage and turn off or delete all that stuff from the ECM.

 

[Rocket Man]

If a new fuel cap doesn’t fix it I just replace both valves and if that doesn’t fix it I replace the charcoal canister. None of the parts are very expensive.

 

[swathdiver]

If a new fuel cap doesn’t fix it I just replace both valves and if that doesn’t fix it I replace the charcoal canister. None of the parts are very expensive.

There's a hose underneath over the tank that's $130, so it could all exceed $500 if one shotguns it. The Tech-2 eliminated the purge and vent so it's between the tank and gas cap or something like that.

 

[Doubeleive]

I would just do what Mark said shotgun it with the 3 parts and 99.9% of the time that resolves the problem, without a tech2 and the EXACT right conditions you probably won't find the one particular cause, doing the test with the tech2 is possible but boy it's tricky, you have to hit the buttons at just the right time, maintain a certain rpm, temp has to be right, ugh.

 

[Rocket Man]

There's a hose underneath over the tank that's $130, so it could all exceed $500 if one shotguns it. The Tech-2 eliminated the purge and vent so it's between the tank and gas cap or something like that.

Vent valve is $13, purge valve is $20, canister is $80, all AC Delco. The hoses are unlikely to suddenly start leaking imo. Start with the cheapest of the 3 or do both valves to start.

Edit: I didn’t see where he eliminated the purge or vent with a Tech 2?

 

[Doubeleive]

Vent valve is $13, purge valve is $20, canister is $80, all AC Delco. The hoses are unlikely to suddenly start leaking imo. Start with the cheapest of the 3 or do both valves to start.

Edit: I didn’t see where he eliminated the purge or vent with a Tech 2?

he didn't I was just referencing james

 

[Rocket Man]

Vent valve is $13, purge valve is $20, canister is $80, all AC Delco. The hoses are unlikely to suddenly start leaking imo. Start with the cheapest of the 3 or do both valves to start.

Edit: I didn’t see where he eliminated the purge or vent with a Tech 2?

Sorry @swathdiver I didn’t see that you were chasing this problem also. Thus my confusion. Carry on. Those prices were for the OP’s 05.

 

[Rocket Man]

I have also been chasing this stupid problem forever it seems like. The problem for me is that I can check the functions of the valves but there’s no way I could see by using the Tech 2 to see if there was a leak at them. Mine was a small leak also whatever that means, and the code pops up so randomly. Sometimes it’s a month or two or three. I had replaced both valves and thought it was fixed but 3 months later it came back. So I just replaced the canister last week, and in the process I found a pinched hard plastic line that must have happened when I dropped the fuel tank to change the fuel pump. I fixed the line by splicing in rubber fuel hose. I won’t know if I fixed it for at least 3 months lmao.

 

[swathdiver]

I would just do what Mark said shotgun it with the 3 parts and 99.9% of the time that resolves the problem, without a tech2 and the EXACT right conditions you probably won't find the one particular cause, doing the test with the tech2 is possible but boy it's tricky, you have to hit the buttons at just the right time, maintain a certain rpm, temp has to be right, ugh.

On the GMT900s the test is run cold with the motor off. ECT has to be below 158 degrees, I found out the hard way trying to help a fellow member and his truck was too hot and those little 500 watt fans on his would kill the battery before bringing the temp down so we resigned to run it another day.

 

[ueww40]

I came to the same conclusion. since I didn't see any smoke leaks I will assume for the time being that all the tubing and lines are ok. The 3 suspect parts (purge valve, vent valve, gas cap) all OEM are on order from Rock Auto totaling $55 and should be here by the end of the week. Will then replace them one by one and see which fixes the problem, if it does fix the problem. If not back to the think tank. Will keep you all posted. Thanks for all the great info.

 

[Big Mama]

Same here. It’s frustrating bc you change a part code goes away so you think you’re good only to have it come back 2 weeks later. I got lucky in that the hose to my tank was split and came off so I could see the problem but not before a gas cap and purge valve but heck they were 12 yo too.

 

[Summajet]

Mine did same on my 03 flex fuel Yukon and it was the solenoid on driver rear side above gas tank.

 

[ueww40]

I replaced the gas cap, the purge valve and the vent valve and drove it over 120 miles in 3 days with the hopes that the computer decides that the small leak was fixed and turned off my check engine light, but the check engine light is still on. So I was just about to give up and take it to a shop. Today I went to Advance Auto Parts and ask the guy there to do another reading of my error code to make sure that it is still the same and to my surprise he told me that the computer WILL NOT TURN OFF the check engine light, even if the problem has been fixed. Now that would be horrible. IS THAT TRUE? He said that the only way this check engine light goes away is by resetting it, which he did. Now let's see if the light comes back. This problem may have been fixed weeks ago unbeknownst to me thinking the light goes out when it's fixed.

 

[Rocket Man]

I replaced the gas cap, the purge valve and the vent valve and drove it over 120 miles in 3 days with the hopes that the computer decides that the small leak was fixed and turned off my check engine light, but the check engine light is still on. So I was just about to give up and take it to a shop. Today I went to Advance Auto Parts and ask the guy there to do another reading of my error code to make sure that it is still the same and to my surprise he told me that the computer WILL NOT TURN OFF the check engine light, even if the problem has been fixed. Now that would be horrible. IS THAT TRUE? He said that the only way this check engine light goes away is by resetting it, which he did. Now let's see if the light comes back. This problem may have been fixed weeks ago unbeknownst to me thinking the light goes out when it's fixed.

You have to either clear the codes with a scanner or perform a certain amount of drive cycles without any issues. That number depends on the code. Get yourself a cheap $20 scanner that can read and clear codes. It’s well worth the money. FYI this is nothing new.

 

[HiHoeSilver]

I replaced the gas cap, the purge valve and the vent valve and drove it over 120 miles in 3 days with the hopes that the computer decides that the small leak was fixed and turned off my check engine light, but the check engine light is still on. So I was just about to give up and take it to a shop. Today I went to Advance Auto Parts and ask the guy there to do another reading of my error code to make sure that it is still the same and to my surprise he told me that the computer WILL NOT TURN OFF the check engine light, even if the problem has been fixed. Now that would be horrible. IS THAT TRUE? He said that the only way this check engine light goes away is by resetting it, which he did. Now let's see if the light comes back. This problem may have been fixed weeks ago unbeknownst to me thinking the light goes out when it's fixed.

Certain codes will go away and the light will go off on its own, but it may take something like 50 drive cycles to do so. Some will not go away unless cleared by a scanner. I'm not sure which category the evap codes fall into, but I do seem to remember my po449 light going away and then coming back on its own at some point...