Charcoal Cannister And Vacuum Switch Valve

[Geno]

Can anyone tell me where the Charcoal Cannister is on my 99 Lexus RX 300 also can anyone tell me where I can get a vacuum switch valve for this vehicle. I am still trying to get my check engine light off due to the last and only code = P0446. has anyone had this problem?

Geno K

[Thienn]

I don't know where the charcoal canister for the RX is but if you know where the Vacuum Switch Valveis then it should be easy to trace it back. The Canister is connected to the VSV so just follow the hose backward and you will find it (it usually locates by the firewall). I have the same check engine light for the same code (Evaporator) with my 1996 SC400; took me awhile to figure it out. So here we go:

-Check your gas cap and make sure it is still nice and tight; it should make a suckling noise when you open the cap. If not, replace the gas cap gasket (less than 5 buck.

-Get a volt meter and check the resistance between the two terminal! It should be between 27-33 ohm when cold (room temperature) if not it should be replaced. Also check it when hot (after driving for half an hour or so) or put it in a 90 degrees C oven (make sure you clean it throroughly to get rid of the gas vapor) or it will catch on fire. I put it on a convection oven at work so I don't have to worry about spark. If it is anything over 35 ohm then it should be replaced. This was the problem with my VVS; the resistance goes up as it getting hotter.

-You could also check the canister but I doubt it is the cause of the problem. The ECU is sensing the current (resistance) thru the VVS and give the warning light so check the VSV first and replace it if neccessary! The VSV is only 50 bucks (with Free Shipping from Plano Lexus; the dealer will charge over 80 bucks plus tax) and the canister will set you back over 250 bucks so whatever you do change the VSS first. I did all these and found that my VSS' resistance would goes up as it gets hot. I replaced it and reset the ECU; the check engine light had gone for over 6k miles

-Also, replace the PVC while you at it (it should locate on the valve cover somewhere).

I hope this help to fix your problem! Thienn

[Geno]

I don't know where the charcoal canister for the RX is but if you know where the Vacuum Switch  Valveis then it should be easy to trace it back.  The Canister is connected to the VSV so just follow the hose backward and you will find it (it usually locates by the firewall).  I have the same check engine light  for the same code (Evaporator) with my 1996 SC400; took me awhile to figure it out. So here we go:

-Check your gas cap and make sure it is still nice and tight; it should make a suckling noise when you open the cap.  If not, replace the gas cap gasket (less than 5 buck.

-Get a volt meter and check the resistance between the two terminal!  It should be between 27-33 ohm when cold (room temperature)  if not it should be replaced.  Also check it when hot (after driving for half an hour or so) or put it in a 90 degrees C oven (make sure you clean it throroughly to get rid of the gas vapor) or it will catch on fire.  I put it on a convection oven at work so I don't have to worry about spark.  If it is anything over 35 ohm then it should be replaced.  This was the problem with my VVS; the resistance goes up as it getting hotter.

-You could also check the canister but I doubt it is the cause of the problem.  The ECU is sensing the current (resistance) thru the VVS and give the warning light so check the VSV first and replace it if neccessary!  The VSV is only 50 bucks (with Free Shipping from Plano Lexus; the dealer will charge over 80 bucks plus tax) and the canister will set you back over 250 bucks so whatever you do change the VSS first.  I did all these and found that my VSS' resistance would goes up as it gets hot.  I replaced it and reset the ECU; the check engine light had gone for over 6k miles

-Also, replace the PVC while you at it (it should locate on the valve cover somewhere).

  I hope this help to fix your problem! Thienn

←

Thank you so much. You have been a great help. I will follow your protocol and keep you posted.

Geno K

[blk_on_blk]

Okay, so I know this is an old post, but I'm finding I have the P0446 code recently. I don't know if it's tied in with the P0446 code I just got the other day (a bad coil), but I've done some research on it and it's a mess. I know there is a TSB (EG001R-99 [APR 99] Diagnostic Trouble Code P0446), and i haven't checked that yet, but I've read a ton of threads on this... everything from in here with the RX to other sites with Camrys, Corollas, and Tundras. Sounds like this code is a buggar for many people.

So, I guess my question is if any main culprit has been found with this code? From what I've found, it could be these problems, in order of likely cuprits:

1) CCV= Closed Canister Valve

2) VSV = Vacuum Switch Valve (tank bypass valve)

3) VCV = Vacuum Control Valve

4) Charcoal canister unit

5) everything else from an internal leak in the canister (which I guess would be item 4) to kinked hoses to a crack in the system somewhere to a clogg in the system (which seem to come with codes P0440 and P0441).

What a nightmare to diagnose. I know, there could also be the potential of a loose gas cap, but I've read where that also trips the additional EVAP codes of P0440 and P0441.

I've also read where there is a bulletin on the 1999 model year where there is a phantom reading that self-corrects... what the heck?

So do I wait to see if it self-corrects after I replace the coil?

Someone else on this board said there may be an emmisisions repair recall on this specific problem... anyone know about that? I know about the TSB, and have yet to read it, but if there is a recall, that would be nice to be able to take it to the dealer under the recall and have it fixed.

Any suggestions... other than "good luck"

[lenore]

I know that they had to replace my charcoal canistor on my 99 many years ago for that problem. It fixed it. But It is frustating when you are trying to diagnose it. good luck

[blk_on_blk]

Thanks for the reply, Lenore. I hear that when you purchase the replacement canister, it comes with some of the valving like the VSV (or VCV... I can't remember which one is on the cansiter) and purge valve, so getting a new canister is kind of like a catch-all in that it replaces most of the major components in that area (which I'm guessing is why it's a few hundred dollars for the part). I was thinking about doing this, but I've read when the problem is in the canister, you get all three codes reading (0440, 0441, and 0446), but I'm hoping with just the one code reading, it's something else like one of the valves.

From what I've read, the 0440 code is from a 'large leak', like a crack in a component, or something to that nature. If it's the 0441 code, then it's a small leak and reading 'improper purge'. The 0446 is suposedly something in the vent control system. BUT, I've read where people have gone through and individually replaced each component and nothing cures the codes except for replacing the whole unit. Soooo... that just leaves me unsure of how to approach it. Also from reading it doesn't seem the dealers have a real good grasp on diagnosing the problem either, other than the smoke test and some proprietary diagnostics tool... with all the diagnosing and labor, I might be better off cost wise just buying the full canister and installing it myself.

It doesn't sound like this is a major problem, so I'll do some more research and see what I can find out. Thanks again for the reply... every bit helps.

Oh, one last note on this, my RX passed emissions with flying colors a week or so before this problem showed up.... so, I don't really know what I should take from that. Does that mean a sticky valve, but everything else is working okay? This ones got me a little lost. I hate to replace parts that don't need replacing.

[lenore]

You know maybe just cleaning the canistor valves might work. By the way the carbon canistor is back by the fuel tank and it does have external pressure valves that feed the ECU. It is on page 1817 on the RX300 repair manual...Search this site for the download of a RX300 repair manual.

[rmk9785e]

On 5/17/2007 at 7:04 AM, lenore said:

You know maybe just cleaning the canistor valves might work. By the way the carbon canistor is back by the fuel tank and it does have external pressure valves that feed the ECU. It is on page 1817 on the RX300 repair manual...Search this site for the download of a RX300 repair manual.

I realize this is 16 years old thread but the RX300 is a hardy vehicle as is its P0446 code. Even with all the discussion, there is no step by step troubleshooting guidance.

Where can one access the RX300 repair manual and this TSB (EG001R-99)?

[unknwn]

I'm working on a 2001 RX, and the vacuum switch valve(?) is an entirely different animal vs. the info supplied in the '99 version of the manual. 

I found the switching valve under the hood, plugged into a revised air box lid. The valve on my car was broken and severely buggered up with a stack of unrelated fittings and what seemed like a -mile- of black tape. I've since found some replacement parts to make things -whole- again in that area, but would really appreciate some access to repair manual pages that reflect this tremendous change from inception ('99) to the revision ('01) models.

[unknwn]

"...to the revision ('01) models "

I've since, found this revision on a '00 model I found in a boneyard.

[gaylestorm]

This post is dated 2004, but I'll reply.  Based on what I read, PO440 Vapor Pressure Sensor and PO446 is the charcoal sensor. Check hoses for cracks. Remove fuse 20amp yello under hood, use the white tool provided on the box lid; remove for a minute or two and return tool to lid. Do not fill tank with gas.. keep at low level... the charcoal filter will clear itself.  Hope this helps someone.