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Discussion Starter · #1 ·
So over the last two weeks, I've had a check engine light. I used TorquePro to determine that it was P0451 (Evaporative Emission Control System Pressure Sensor Range/Performance). After a google search, it looks like it can happen from one of the things below:
  • A defect in, or damage to, the gas tank
  • A problem with the fuel tank sending unit
  • A faulty fuel tank pressure sensor
  • An open or shorted fuel tank pressure sensor circuit
  • A faulty canister vent valve (somewhat rare)
  • A faulty PCM (rare)
Even though I didn't have a P0400 (gas cap), I inspected mine and decided to replace it and cleared the code. Check engine light came back. I left it on this time and it seemed to clear on it's own after driving (and refilling the tank) some miles. Now it's back.

With the miles I have I guess it could be any of the above. Hoping it is an easy find if I take it in.

Besides the above things (and not dropping the gas tank), are there any other things I could try that are fairly cheap on my own? Any way to inspect the tank pressure sensor without dropping the tank? I called a local shop (not dealer) to see what it might cost me, but they didn't want to commit to a price until they looked the vehicle over and did their own diagnostics.
 

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You say "faulty canister vent valve (somewhat rare)." If you mean the purge valve, it's very common. Many, many threads here about replacing it.

There is a a component in/near the gas fill line that IS rare (I can't recall what it's called). I don't know much about it. Maybe rbarrios or another smart person will weigh in on it.
 

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Discussion Starter · #3 ·
You say "faulty canister vent valve (somewhat rare)." If you mean the purge valve, it's very common. Many, many threads here about replacing it.

There is a a component in/near the gas fill line that IS rare (I can't recall what it's called). I don't know much about it. Maybe rbarrios or another smart person will weigh in on it.
Thanks for responding greentraverse, sorry, that was a copy/paste from a google search on P0451. I thought it might be the purge valve actually. I figured it might be wiring/insulation or shorting possibly or just a bad valve due to the miles on my car. There is a valve up front that tends to fail if you over fill the gas tank. I did over fill the gas tank the first few years I had this vehicle and I had to replace that valve (easy) and then replaced it maybe 3 years ago again. The symptoms are what sounds like flooding when you try to start the vehicle. You have to floor the gas pedal to start it. Any chance it might be this valve again? I don't want to spend another $50 to $60 and it not be that valve. No way to replace the purge valve without dropping the gas tank I guess?
 

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The valve up front is the purge valve. I think it might be the valve.

I know the valve was re-designed (it has a new PN) a few years ago. Mine was replace about 18 months ago under warranty.
 

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$50-60?
the valve up front is $14 to $24 on rockauto. depending on brand. check shipping. then go back and add some clearance wipers, oil filter etc until the shipping price increases. then back off an item.
then look on here or the web for Rock auto discount code.

the valve on the tank- im trying to remember what its called. It does fail, but way less than the one up front.
It also sets a P04XX code. Ill see if I can find a similar post
 

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the one up front is called the Vapor canister PURGE valve.
the one by the tank is called the Vapor canister VENT valve.


this is what the part looks like- (this is the Dorman part)

 

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Discussion Starter · #7 · (Edited)
Thanks all. So I took my vehicle to Tires Plus for alignment (bought a lifetime contract with them years ago -- its paid for itself) and decided to have them do a diagnostic on this for me for $99. Came back with the Evap Purge Solenoid valve. I've replaced that maybe 2x already. 3 years ago and then 3 years before that. So I told them I'll replace it myself (noticed the part on Amazon for $25, but I might buy it from 1A Auto if it is reasonably priced). It is very easy. After replacing it, I have an oil and air filter replacement coming up anyway, so I'll do that and buy some intake manifold spray and take the big hose off and look for the milkshake (last time I checked, it wasn't so bad) and clean it out if needed and clean off the intake manifold as well. I did the modification of drilling out the PCV valve a few years ago, which resulted in less milkshake. Tires Plus recommended a fuel system cleaning. is there any additive i can add to the gas to help on this?

What's interesting on this is that the times before, one time it gave me a check engine light, but not the second time. Both times before, I knew it was probably this valve because when I would start the car (first time on a cold start or just after filling up), it sounded like it was flooded and you had to press the pedal to the floor to start it. Not this time. I guess there are different symptoms for when this solenoid valve dies.
 

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Discussion Starter · #8 ·
Thanks all. So I took my vehicle to Tires Plus for alignment (bought a lifetime contract with them years ago -- its paid for itself) and decided to have them do a diagnostic on this for me for $99. Came back with the Evap Purge Solenoid valve. I've replaced that maybe 2x already. 3 years ago and then 3 years before that. So I told them I'll replace it myself (noticed the part on Amazon for $25, but I might buy it from 1A Auto if it is reasonably priced). It is very easy. After replacing it, I have an oil and air filter replacement coming up anyway, so I'll do that and buy some intake manifold spray and take the big hose off and look for the milkshake (last time I checked, it wasn't so bad) and clean it out if needed and clean off the intake manifold as well. I did the modification of drilling out the PCV valve a few years ago, which resulted in less milkshake. Tires Plus recommended a fuel system cleaning. is there any additive i can add to the gas to help on this?

What's interesting on this is that the times before, one time it gave me a check engine light, but not the second time. Both times before, I knew it was probably this valve because when I would start the car (first time on a cold start or just after filling up), it sounded like it was flooded and you had to press the pedal to the floor to start it. Not this time. I guess there are different symptoms for when this solenoid valve dies.
 

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Discussion Starter · #9 ·
This is the purge valve on Amazon for $14:
10468


Thinking about replacing the hose that connects to this as well, just not sure what that part is called exactly. Anyone know?
 

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I'd put the GM part in, cheap knock off stuff doesn't last.
 

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Discussion Starter · #13 ·
I'd put the GM part in, cheap knock off stuff doesn't last.
Well, the last two I put in 3 years ago and maybe 3 years before was AC/Delco (around $60) from dealer as I couldn't find it anywhere else. I'm thinking it's kind of a wash.
 

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This is the purge valve on Amazon for $14: View attachment 10468

Thinking about replacing the hose that connects to this as well, just not sure what that part is called exactly. Anyone know?
I'd be careful about ordering any automotive parts from Amazon. It's a crap shoot on what you'll be getting, even if it says GM part. This one probably a Chinese knock-off. Put in the GM part. If you want to order online, Rockauto.com. They have the GM part and the Standard Motor Part (order the Blue Streak version, not the T series. Standard Motor Products makes a lot of the OEM parts for some of the car manufacturers. "The cheapest is not always the least expensive".
 

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Discussion Starter · #16 ·
I'd be careful about ordering any automotive parts from Amazon. It's a crap shoot on what you'll be getting, even if it says GM part. This one probably a Chinese knock-off. Put in the GM part. If you want to order online, Rockauto.com. They have the GM part and the Standard Motor Part (order the Blue Streak version, not the T series. Standard Motor Products makes a lot of the OEM parts for some of the car manufacturers. "The cheapest is not always the least expensive".
One problem with Rockauto is the delivery to Colorado. There is an issue here since the different locations (towns) pay different sales tax. Rockauto stopped delivering to Colorado a couple years ago, so I don't order from them anymore, plus I don't care for their part search. I do like 1A Auto as they will look up the parts to make sure they are the correct items based on the VIN, but they are a little slow on customer service.

So, this is the third purge valve I've had to install. The last one was 3 years ago, the first one was maybe 3 or 4 years before that. both of those I had to buy from the dealer for about $60 because I couldn't find them anywhere else. The one I just pulled off (bought from the dealer) was a Bosch, not AC Delco. I found the redesigned AC Delco valve online through both Amazon and Walmart and were about the same price, so I ordered through Walmart and installed it yesterday. We'll see if it fixes P0451 (might actually be the canister on top of the gas pump). I cleared the error/check engine light and am driving it now.
 

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One problem with Rockauto is the delivery to Colorado. There is an issue here since the different locations (towns) pay different sales tax. Rockauto stopped delivering to Colorado a couple years ago, so I don't order from them anymore, plus I don't care for their part search. I do like 1A Auto as they will look up the parts to make sure they are the correct items based on the VIN, but they are a little slow on customer service.

So, this is the third purge valve I've had to install. The last one was 3 years ago, the first one was maybe 3 or 4 years before that. both of those I had to buy from the dealer for about $60 because I couldn't find them anywhere else. The one I just pulled off (bought from the dealer) was a Bosch, not AC Delco. I found the redesigned AC Delco valve online through both Amazon and Walmart and were about the same price, so I ordered through Walmart and installed it yesterday. We'll see if it fixes P0451 (might actually be the canister on top of the gas pump). I cleared the error/check engine light and am driving it now.
 

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Discussion Starter · #19 ·
So about 2 weeks later after replacing the purge valve and clearing the code, still no re-occurrence of the check engine light (I'm knocking on wood here). I need to do an oil change and air filter change this coming week or so and I will check the for any milkshake and clean it out if necessary.
 
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