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Silverado Check Engine Light

billti's Avatar
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September 19th, 2006, 12:45 AM   #1  
Silverado Check Engine Light

The Check Engine Light (CEL) on my 2004 Silverado keeps coming on about every 6 months. The code (P0442 I think) is for a small gas tank evaporation leak or a gas cap not sealing. I am careful to tighten the gas cap after filling up. The truck is still under warranty, and the dealer "fixes" it every time, but it is inconvenient and I am concerned about the cost of repair when the warranty runs out. The dealer has replaced the gas cap at least twice. Is anyone else having this problem with the Silverado? Any suggestions? And will the vehicle pass the safety inspection with the CEL on?

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September 19th, 2006, 1:38 AM   #2  
RE: Silverado Check Engine Light

not me

uncle bill's Avatar
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September 19th, 2006, 2:15 PM   #3  
RE: Silverado Check Engine Light

The gas tank is vented through the cap and through a seperate vent tube ( I think ). If the vent tube becomes clogged or dislodged, it may set the code. Make sure the new cap isn't faulty.

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December 2nd, 2008, 10:45 AM   #4  
RE: Silverado Check Engine Light

Take that thing back to the dealer and tell them they sold you a lemon. I have the same issue on my 2004 and it has done nothing but cost me thousands of dollars. As soon as the truck was out of warranty, they washed their hands of it and I was left holding the keys to a piece of junk. I have been a Chevrolet person since 1986 but after this fiasco, will never buy GM again. I contacted Chevrolet and guess what?? they told me that they could not help. I went through the exact same issue as you described with the exact same outcome. Unload it fast. I will be the first in line when the class action law suit starts. I should also add that the vehicle will not pass an emissions test unless the light has been off for more than three weeks. I was told that this issue was no big deal, but no big deal to them and me are obviously two different things. It has cost me a new transmission, new four wheel drive system and NUMEROUS trips to mechanics. Unload it as fast as you can!!

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December 4th, 2008, 10:32 PM   #5  
RE: Silverado Check Engine Light

The GAS CAP code!!!!!!!!!!!!!! [/align][hr]


The dreaded GAS CAP code!!!

I see many posts here about how to fix ( the dreaded GAS CAP) EVAP codes. Today I am going to educate you as to the functions and diagnostics involved in Evaporative Emissions issues and what the codes mean.
Lets start off with the whys.
The purpose of the Evaporative Emission system is to limit the amount of Hyrdocarbons released into the atsmosphere.
Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid OFF, fresh air is drawn through the vent solenoid and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.
So in a nut shell if the control module senses a leak in the system that will allow more than a prescribed amount of fuel vapors escape, the module will illuminate the yellow engine light also know as the Check Engine (CEL)or Service Engine Soon (SES) light.
Depending on the year, make and model of your vehicle, this leak could be as small as .020” or twenty thousands of an inch ( a hole equal the point of a sharpened pencil lead)

Now with any diagnosis, the first thing we what to do after verifying the concern is to check the codes. This can be done at just about any chain auto parts store or if you own a code scanner, you can do it yourself.
DO NOT CLEAR THE CODE!!!!!!!!!!!!!!!!!!!! This is your key to finding out what is going on……we will clear the code after we repair the vehicle.

EVAP codes are considered either TYPE A or TYPE B codes..which in simple terms means the control module must see 1 failure for a TYPE A or 2 or more back to back failures for a TYPE B before the SES or CEL light is turned on.
Lets take a look at the codes and what they mean
P0440 or a P0455 – This is a Large leak indication or as people call it “The GAS CAP code”
This is a TYPE B code. Usually the code is caused by the gas cap being left off or loose after a refuel. This code could also be caused by any failure of the EVAP system that will cause a large leak.
P0442 – This is a Small leak indication.
This is a TYPE A code. This indicates a leak as small as .020”.
This code needs some serious diagnosis and knowledge of the system to find and repair the leak. Usually specialized equipment will be used to identify the leak.

P0446 – This indicates there is a restriction or blockage of the Vent Solenoid.
This is a TYPE B code. Any thing that prevents the venting of the EVAP system will set this code…usually dust and debris in the Vent solenoid or a damaged vent hose will cause this.

The other EVAP codes (P0443,449 etc) are electrical codes related to various components of the EVAP system.
Electrical codes need some good diagnostic skills, knowledge of the system and some specialized equipment.

With any car repair concern, there is a logical flow to follow when trying to identify what is going in the GM world, we call it Strategy Based Diagnostics or 7 simple steps to diagnose a concern.
As always, verifying the concern and then doing a thorough visual inspection is key. It’s amazing how quickly a problem can be fixed by just the results of a visual inspection.
Now getting back to EVAP concerns….once you have identified the problem, you must come up with a repair, then a verification that the vehicle is repaired properly.
With EVAP leaks, usually a large leak is caused by a loose gas cap. Reinstalling the cap and clearing the code will be a quick remedy. But remember that you must always verify your repair..this could include professional intervention…(EEK!!!!!!!!!PAYING SOMEONE TO WORK ON MY CAR…..NO WAY!) . Well yes, this may be necessary..I have seen many times where people have come in to have a EVAP code cleared and refuse diagnosis only to have the light come back on…then blame me for the light coming back on…(then post on AF how the “stealership” did not fix their car).
But this isn’t a rant, this is information on what is going on.
Repair verification could include EVAP system testing with specialized equipment to verify that there are no leaks present..I personally check every EVAP system for leaks even if I find the customer left the gas cap loose…this insures that there are no other problems with the system that would cause the customer a trip back to see me. Far too many times have I seen someone tighten a gas cap and clear a code only to have the vehicle come back a few days later with a “real” EVAP leak…masked by a loose gas cap.
If you have a SES or CEL light caused by an EVAP concern and you have the code cleared and it comes back on after a few days….get to your local repair shop ( I recommend your local dealer with factory trained technicians) and have the system tested and repaired properly.
If you want to DIY the repairs, feel free, there are plenty of resources on the internet, but just don’t jump in and replace parts…educate yourself on the system and perform some diagnosis…many times a part will not fix the concern…
Good Luck

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April 2nd, 2009, 10:18 AM   #6  
Really good info

Thanks ukrkoz
This is what this forum should be. I find too many rants.
I have a 2002 silverado (best truck I have had in 40 years), 8.1 gas, and have occasionally had a service engine light. I just purchased a scan tool and trying to learn how to use it, and feel confident that I will. Your info will surely be helpful, so Thanks again.

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November 4th, 2009, 2:49 PM   #7  
P0455 Code

Thanks for your post.
I took my 2005 Silverado Crew Cab 5.3 to the local dealer today with the code P0455 and they replaced the open vent solenoid valve. Hopefully this fixes my problem.
Again I like your explanation of a systematic approach to trouble shooting a problem and resolution of the same.

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February 25th, 2010, 7:28 PM   #8  
Did open vent solenoid valve fix it?

TexasM ....I know it has been 4 months since the post but I am hoping to find out if the open vent valve solved your problem? And, is it a pricey fix?

I have a 2006 Silverado Z71 Ext Cab and I LOVE THE TRUCK !!!! I have been and ALWAYS will be a Chevy man!

However, I have been getting the Tighten Fuel Cap message and then the CEL lights comes on after a few warnings. I replaced the gas cap with a GM cap so no messing with after market junk but after just 200 miles with new cap the warning message came up again today.

Unfortunately, my usual dealer that I completely trusted closed as part of the GM cutbacks .... so I am not as ready to jump in and go to another dealer.

thanks for your time

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February 26th, 2010, 8:45 AM   #9  
Check Engine Light problem resolved

sorry for not getting back to post a follow up on my check engine light problem. Apparantly that was the problem because I have not had the check engine light back on since it was repaired, and as you stated, it was expensive, over $300.

On another note, my next door neighbor has a 2004 Chevy Silverado, and his check engine light had been on for over a year,,,,hahahaha, he doesn't let small things bother him as much...
anyway after telling him about my repairs (and the fact he was needing to pass state inspection) he took his to our local dealer (Ron Craft Chevrolet) and had the same fault code. After changing his solenoid he also has the problem corrected.

Good luck on your as well, seems this must be a common item and wonder if a recall would be a better way to correct.

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February 27th, 2010, 5:38 AM   #10  
Thanks for the reply TexasM. I have been doing some more research and found out something that I am hoping you might be able to confirm. Was the repair costly because they had to drop the transmission to be able re-run the hoses for the solenoid? I am told that the solenoid for the Silverado is the same one for the Cavalier with the difference being how the part is sold. The silverado one is sold as a package with new hoses and things when all that really needs to be done is a swap out of the actual solenoid. The mechanic I spoke to about this finding is researching it himself to validate.

Thanks again for the reply and Go Chevy!

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