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Old 06-02-2022, 12:56 PM   #1
Inept
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2002 SL
Default P0446 Code Fixed

I mentioned in my P0401 thread that once I fixed that issue I had a P0446 pop up.

This one is called: evaporative emission control system (EVAP) vent control circuit malfunction

I spent some time here and there fiddling with it, trying to narrow down the problem, and finally decided to drop the tank and pull the tank pressure sensor.
After a while of driving around (stupid 30 MPG...) to use up most of the gas, I finally raised the car and got the tank down enough to get the sensor off.

**Pro Tip** To get to the sensor, it's not necessary to fully drop the tank, or even disconnect the hoses on the driver's side.
Make sure the car is up as high as you can get - I had the bottom of the gas tank over 18" off the ground - the tank straps are secured at the front & pivot, so they're your limiting factor for how far the tank can go down.

Just remove the tank strap bolts & free the tank straps. Pull them all the way to the ground, then grab the front passenger side of the tank & pull it down as far as it can go. that should give enough room to get a hand up there to the sensor.
The sensor has an easy to remove electrical connection (push the raised tab on top toward the rear of the car) & clip the zip tie holding the sensor on.
FDRYER has a nice diagram HERE of how the sensor is attached to the tank. It's helpful to know what to do when you're not looking at it directly.
The sensor is in there pretty good, you have to wiggle it & maybe gently pry with a screwdriver to pop it out once the clips are undone.

Once I knew what I was doing, it took me about 5 mins to pull the one on the junkyard car.

Bench testing the original showed that there was no voltage change on the signal pin - showed 5V all the time at atmosphere, with pressure & with vacuum.

Eventually I was able to make it over to a pick a part place, and got a front side marker, a rear tail light lens and a sensor all for $20!

This JY sensor showed a few volts at atmosphere, and changed with added pressure or vacuum!

Put it back in the car, put the tank back & started driving around. Eventually after about 5 drive cycles, all DTCs showed as completed on my scanner with no SES light!! Finally!

So on my way to get my emissions checked, of course I got a nice rock chip in my pristine windshield. Figures.

But the emission test passed & I'm good to go! Fuel tank pressure sensor was the culprit!

I hope this helps someone!

Inept
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Old 08-09-2022, 01:42 PM   #2
newsan
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Default Re: P0446 Code Fixed

Nice writing!
Do you still remember the pressure sensor voltage reading when in the air pressure with 5V supply? Is it about 1.5V?
Are the pressure and the voltage output in positive correlation? The voltage reading is less when vacuum and more when adding pressure.
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Old 08-10-2022, 06:40 PM   #3
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Default Re: P0446 Code Fixed

Hmm, I don't remember right off hand, but your description sounds correct- though I may be remembering the MAP sensor- It seems like both map & Tank pressure sensors should act similarly, though the pressure ranges are different.

I tried to look around, but I think I got rid of the paper I'd recorded the values on.

I seem to remember that I found a website describing it also - Might have been Low Saturn's site, but I didn't see anything fromw a quick glance.

Sorry I can't be more helpful!
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Old 09-02-2022, 08:34 PM   #4
termite
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Dizzy Re: P0446 Code Fixed

Inept, I have been dealing with this P0446 Code over a year now. I first found a loose vacuum line at the throttle body that goes to the purge valve. I cleared the code, and it was gone for 3 months.

Then it came back so I replaced the gas cap that was around 15 years old. It still came back, so I replaced the vent valve which seemed to test okay after I put the new one on.

I used an Xtool D7 scan tool, and found I was able to command it on and off. I used this "EVAP service bay test" and monitored the fuel tank pressure sensor and it seemed to be changing in value from 1.6 to 3.2 volts.

After a while of the car being on, I tried testing the vent valve again, and it wouldn't respond. I did the EVAP service bay test again and saw that the fuel tank pressure sensor output was stuck around 4.8 volts.

My question is, could the fuel tank pressure sensor be going bad, or do I have a bad connection at the electrical connector. I was thinking of dropping down the tank like you did, and try reseating the connector before buying a new sensor.
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Old 09-16-2022, 06:52 PM   #5
Inept
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Default Re: P0446 Code Fixed

I think if I was going to drop the tank, I'd probably just replace the sensor. If you're doing it on the ultra cheap, a reseat might be worth a try, but I've always been impressed with the construction of those weatherpack connectors, especially protected like it is on top of the tank. I'd suspect the sensor before the connection as long as it hasn't been messed with before.

I got my sensor from a junkyard for like 10bucks so that's the super cheap version, just one level up from ultra cheap.

Good luck!
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Old 09-21-2022, 01:31 PM   #6
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Default Re: P0446 Code Fixed

Inept, I decided to get a new GM fuel tank pressure sensor, P\N 16238399 to replace the old one. I lifted the car and looked underneath and watched a YouTube video from Rainman Rays where he had to drop the tank to replace the fuel pump in a similar SC1. He has great videos that you should check out!

https://www.youtube.com/watch?v=Jd0kxTRB7Mo

I then decided to have a trusted mechanic who does my car inspections change the part out for me. I ran the car until the low fuel light came on to make the job easier for him. I dropped it off today, so I will see how it goes.
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Old 09-26-2022, 10:22 AM   #7
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Default Re: P0446 Code Fixed

Inept, I just got my car back from the mechanic. He charged me $272.95 to install my new sensor. I feel it was well worth it not having to deal with dropping down the fuel tank. Now I will ride around to check to see if the emission readiness tests are complete and the SES light stays off.
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