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99rx300 Check Engine P0440 Code

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My 99 RX300, 31k miles. The Check Engine light came on. I tightened up the fuel cap until it clicked. I took it to autozone, ran the ODBII test, got a P0440 code - Evaporative Emission Control System problem.

The owners manual says tightening the fuel cap can fix the problem and "the indicator lamp goes off after running several times."

Is the fuel cap likely the problem?

When would the lamp go off?

If not fuel cap, what can be checked?


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Alldata (www/ indicates several possible causes for this code:

1) Fuel tank cap improperly installed or damaged

2) vacuum hose cracked, disconnected, blocked, etc.

3) fuel tank cracked, "holed, damaged, etc.

4) charcoal canister cracked, holed, damaged. etc.

I have a '99 as well. I had to get a new cap a while back because the o-ring was leaking. It looked tight, but wasn't. I'd try a new cap first (Autozone, etc).

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You can also disconnect the battery (I usually let mine sit for 15 minutes or so) and it will reset the check engine light. If it comes back on, you will know you haven't fixed the problem by tightening the cap. The down side to this is you lose all of your settings (seats, radio, etc.). I did this same thing not too long ago & checked the gas cap was loose and I disconnected the battery & tightened the cap.....and the light went away. Just my prior experience...but if it comes back on I would be sure to get it checked out.

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The po440 is a small leak from Charcoal Canister to fuel filler neck. To properly diagnost this problem, you will need to apply vaccum on the section mention. Then the valve and watch for pressure drop, Also check the gas cap to see if it holds pressure. Having a lexus scanner will also help, it will tell you what condition the vehicle was in when CEL coming on.


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  • 9 years later...

Hi JPI, i think your post has been long back in 2004, but i dont know if you are still active on this site. I have the same problem,
The CEL throws P0440 code, did a battery disconnect and then it comes back within 50 miles of driving, does not come if I drive on the highway for about 350 miles 2 way on the same day. replaced the fuel cap, did a smoke test on the evap test port towards the hose lines to the intake, no leak, did a smoke test from the air filter back to the canister. The dealer shut off the purge valve with his machine connected to the scan port and the smoke was coming from the charcoal canister hose pointing dowward, which is not connected to any other end. Based on this I was told that the charcaol canister is bad and need to be replaced.; it is costing $545. I just want to be sure that the test conducted is correct and the dealer has truly done a root cause diagnostic.

Appreciate your help.



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Did you check the hose that is behind the air filter housing? Sometimes it comes loose after the air filter has been changed or checked. I think my codes were P0440, 0442, and 0446, not sure many years ago.

Good Luck.

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I checked all the hoses including the hose connecting to the canister all seems to be good. I even did a smoke test recently and the smoke was coming from the hose which is always open on the canister after the mechanic shut off the purge valve on the canister. I was told i need to replace the canister, but wanted a second opinion before i replace it to confirm that indeed the canister is the culprit for the P0440 code and nothing else.

Thanks for the reply.

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