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FriendlyMan

I'm running out of ideas with the P0446 emissions code

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2000 Silverado 1500 4.8L V8 260,000 miles

 

P0446: Evaporative Emission System Vent Control Circuit

I have been pulling my hair out trying to figure out how to fix this check engine light code. I have searched this forum and google and youtube a lot and tried many things but so far nothing has worked. It takes 3-6 days for the code to come back.

 

 

What I have done so far

 

1. cleaned all hoses with compressed air, including blowing out the charcoal canister, vent solenoid, and purge valve

 

2. verified the vent solenoid worked. Give it 12v on the leads and it closes

 

3. replaced the vent solenoid and purge valve on the intake just in case

 

4. replaced the charcoal canister and fuel tank pressure sensor

 

5. replaced gas cap with OEM gas cap

 

6. verified that the wire connector at the vent solenoid has power

 

Other than the check engine light I don't have any problems with the truck. No problems refueling....just need it pass emissions for yearly inspection in my state.

 

I don't have access to a smoke test tool but my next idea is to replace all of the evap hoses with 5/8" fuel hose and the tank fill hose. All of these suggestions are what I have read online could be fixes for this code.

 

Thanks

Friendly

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Have you checked the filler neck? I have had to replace mine twice, once it was so bad that it would leak gas while filling it if I wasn't careful and the second time it had a couple pinholes in it.

 

Sent from my SAMSUNG-SM-G930A using Tapatalk

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I looked at the filler neck today and it does look rough on the outside. I might as well replace it since I cant recall ever changing it out.

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Well I replaced the neck and hose and the code came back. I plan on taking the bed off tomorrow morning bright and early and seeing if i can hold 10psi on it and spraying around the system with soapy water to see if I can find the leak. I'm all ears if anyone has any suggestions.

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When I have EVAP errors, Use a compressor to force air into the filler neck. Wrap a rag around the air hose to create a makeshift seal. One person operates the air chuck and one person operates the creeper. Listen for leaks. One time it was a small valve that had melted somehow, and another time it was a leaky filler neck tube (rusted through).

Edited by starman8tdc

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After you pull the bed, wouldn't be surprised that you find a cracked line up there or maybe even rust causing a leak

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Is your fuel gauge accurate? Has to be for the pcm to pass this test. PCM measures the rate of decay after applying vacuum to the system. Too slow or too fast of decay will set code. Fuel level affects how fast vacuum decays.

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Not 100% sure on your truck, but on later trucks, there is another evap solenoid on top of the engine, near the throttle body. If yours has this, I'd replace both this one and the one by the fuel tank. They're pretty cheap to replace and are what causes probably 80% of evap/emissions codes.......

 

I just did one on my old 06 & it was only about $25 or so and only took less than 10 min to replace.

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That would be the purge valve which the op says he changed.

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Alright so an update to this headache.

 

I can't exactly say I know what fixed the problem but I got the evap emissions test to pass without setting the lone P0446 CEL code. I took it and passed inspection yesterday.

 

What I ended up doing was two things. I Re-wired the fuel pump connector wires. When I first replaced my fuel pump on this truck the new fuel pump came with updated connectors that had to be rewired and the old ones discarded. Even though everything else worked normally (including the fuel gauge from what I could tell), I noticed the old wire splices to the newer connectors were green and corroded. So I cut the corrosion out and rewired them.

 

Second thing I was doing was I set up a miltimeter in the cab with a long wire to the fuel tank pressure sensor voltage output. I knew if I could watch the pressure and see the computer attempting the test that it probably wasn't the computer itself. Sure enough I took it on several rides over the week and watched the voltage. ~1.5v bolts was normal atmosphere. 4.5-5v is vacuum and less than 1v was pressurized. I watched it pull vacuum and release to normal atmosphere and pressurize. So I knew the solenoids were working.

 

My best guess is that tbarn was right on the money and for some reason the corrosion at the fuel sender wire was enough for the computer to not accurately read the sender voltage to calculate fuel rate. (I don't know if that's how the computer actually measures that).

 

Anyway it's working now and I look forward to the next 100k miles. If anyone was wondering I could see if the computer completed the evap emissions test using a Bluetooth obd2 reader on Amazon ($20) and a cell phone app called Torque (free).

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