Diagnostic Code P0446

[Geno]

I have done the following to try and find the EVAP problem on my 99 RX 300. It is not the gas cap, and it is not the Vacuum Switch Valve. I have replaced both and still have that damn check engine light. I can reset this code by pulling the EFI fuse or disconnecting the bat cable. It usually returns in about 100 miles of driving and again the code is P0446. Is there any cheap way to check for leaks in the vacuum hosing, gas tank, charcoal cannister etc. I have heard of a smoke test is this expensive? Just trying to get that light off it is driving me nuts. Any help would be appreciated.

[RX in NC]

Sounds as if you've got a very difficult condition to locate. Have you spoken to any Lexus service managers or technicians about it? I know they'll say that you need to bring it in for diagnostics, but if you can get a knowledgeable individual on the phone for a few minutes, they may give you some ideas on where to look next.

I think your best do-it-yourself step right now is to check the fittings and connections on as many of your vacuum lines as you can get to. I wouldn't be surprised if the problem turns out to be a loose connection at a joint rather than a pinhole leak in the middle of a hose somewhere. It may be as simple as replacing a hard-to-find hose somewhere in your configuration. Vacuum leaks can be quite difficult for the average shade-tree mechanic to find, but the next thing I'd do would be to unplug, clean, and reseat every vacuum hose I could get to.

How is your vehicle running? If performance has remained normal throughout your ordeal, you may want to simply monitor the situation until it becomes easier to detect. But I hear you loud and clear - I prefer to find and fix "check engine" light problems just as soon as they come up. Like you, I despise having to stare at that light on the dash. Keep us posted on what you determine and good luck.

[Geno]

It seems to be running fine. I was wandering if this diagnostic code maybe effecting gas mileage? It runs great but I am a little dissapointed that the gas mileage is not as good as I initially thought. I am getting somewhere around 18-19 miles to the gallon does that sound about right? I really appreciate your response and you have been a great help with other things also.

Sounds as if you've got a very difficult condition to locate.  Have you spoken to any Lexus service managers or technicians about it?  I know they'll say that you need to bring it in for diagnostics, but if you can get a knowledgeable individual on the phone for a few minutes, they may give you some ideas on where to look next.

I think your best do-it-yourself step right now is to check the fittings and connections on as many of your vacuum lines as you can get to.  I wouldn't be surprised if the problem turns out to be a loose connection at a joint rather than a pinhole leak in the middle of a hose somewhere.  It may be as simple as replacing a hard-to-find hose somewhere in your configuration.  Vacuum leaks can be quite difficult for the average shade-tree mechanic to find, but the next thing I'd do would be to unplug, clean, and reseat every vacuum hose I could get to.

How is your vehicle running?  If performance has remained normal throughout your ordeal, you may want to simply monitor the situation until it becomes easier to detect.  But I hear you loud and clear  -  I prefer to find and fix "check engine" light problems just as soon as they come up.  Like you, I despise having to stare at that light on the dash.  Keep us posted on what you determine and good luck.

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[RX in NC]

Your gas mileage sounds about right. My wife's a careful, cautious driver, and her 2000 RX300 AWD vehicle averages around 19 to 20 mpg with equal parts highway driving and city driving.

[mikey00]

I have done the following to try and find the EVAP problem on my 99 RX 300.  It is not the gas cap, and it is not the Vacuum Switch Valve.  I have replaced both and still have that damn check engine light.  I can reset this code by pulling the EFI fuse or disconnecting the bat cable.  It usually returns in about 100 miles of driving and again the code is P0446.  Is there any cheap way to check for leaks in the vacuum hosing, gas tank, charcoal cannister etc.  I have heard of a smoke test is this expensive?  Just trying to get that light off it is driving me nuts.  Any help would be appreciated.

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Did you check the vacuum hose behind the air filter box? It's a black rubber hose connected to the top back of the air filter box and it connects to a metal tube about 12" down by the firewall. It is common for this hose to come of the metal tube while checking the air filter. It does cause a check engine light. I am not sure what the code is.