Gas Cap Code Won't Clear - Lexus IS Forum
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post #1 of 10 (permalink) Old 05-06-2016, 06:44 AM Thread Starter
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Gas Cap Code Won't Clear

I don't have the code number for you guys (trying to get it soon), but my gf got a check engine light. Went by Autozone to pull the code and the guy told her "gas cap". It was the only code. Car runs great. We had had this before and the car stumbled and ran funny and had the traction control light. R & R the gas cap fixed that in the past. This is just the engine light alone with no other symptoms.

Interesting part is this started happening immediately after replacing the alternator the other day. Alternator was bad, and the swap out for that went just fine. Car runs great.

Disconnected the battery and the engine light went away for about a day, but now it's back on.

What can I check or do for "gas cap" engine code and the car is running great? I'll post the code as soon as I track it down today. Sorry about that; just trying to get a head start if possible. Thanks guys.
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post #2 of 10 (permalink) Old 05-06-2016, 06:48 AM
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What can I check or do for "gas cap" engine code and the car is running great? I'll post the code as soon as I track it down today. Sorry about that; just trying to get a head start if possible. Thanks guys.
There's not really a "gas cap" cel. There's a cel that tells you the evap system is leaking. Sometimes it's the cap. Sometimes it's something else. If it just started up after it was worked on. I'd be looking under the hood for broken parts.

1 - By the air cleaner there's a solenoid with two hoses going to it.

2 - Near the brake booster there are hoses and a plastic kidney shaped thing and another solenoid. You might have to pull the engine cover off to see it.

Both of those are part of the evap system. The air cleaner one feeds clean air back to the fuel tank. The booster one can feed gas tank fumes into the engine.

You need the code and then need to look the code up in the manual. It'll tell you where to look.
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post #3 of 10 (permalink) Old 05-06-2016, 10:13 AM
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I had a P0440 CEL come on for the same reason. I thought it was the gas cap, so I checked it over and everything was fine. Started looking more into it and found that it was the same as it was on this tread https://my.is/forums/f115/01-is300-p0...53/index3.html After I did this, my code went away and hasn't came back. Hope this helps.
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post #4 of 10 (permalink) Old 05-06-2016, 10:33 AM Thread Starter
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I'm pretty sure this is something I did during the alternator swap. I pulled one of the hoses lose around the area of the air cleaner box and I think I may have reattached it to the wrong item. There's what looks like a metal vacuum port coming off the engine on the front right corner in that air box area; I thought it went there. But I also had a tube running up the right side of the engine compartment that was open ended. The tube ends right around the anti skid box/manifold area. I had never noticed this before. Sorry...I know I need to post some pics for stuff like this but the car isn't here at the moment.

Ek9B18...GF just informed me the code was P0440.

...and while searching the post allturbo provided, I don't think mine's that valve due to the timing other maintenance, but I did see a pic in the thread and now I'm pretty sure I have this hose ran to the wrong location, as I just mentioned above.
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post #5 of 10 (permalink) Old 05-06-2016, 12:46 PM Thread Starter
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And I was wrong...it's a P0430.
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post #6 of 10 (permalink) Old 05-06-2016, 02:53 PM
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And I was wrong...it's a P0430.
Yeah that's a "I have a bad cat" in bank 2 cel. I'd clear it and see if it comes back.

P0440 is an evap cel. It's like a generic code though the manual suggests there should be other supporting CEL's if you get that one.
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post #7 of 10 (permalink) Old 05-07-2016, 09:45 AM Thread Starter
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So I did have the hose from the solenoid mounted on the air box ran to the wrong place. Fixed that and reset. So far, two days and 70+ miles with neither code coming back.
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post #8 of 10 (permalink) Old 05-07-2016, 04:50 PM Thread Starter
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We'll crap...I spoke too soon. It came back today...still a P0430. There's got to be something going on. Just too much of a coincidence I started getting this code immediately after the alternator swap. I had to have done something or this triggered something.

Anything residual I could check that would potentially give you this one??
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post #9 of 10 (permalink) Old 05-07-2016, 06:03 PM
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For code P0430, look for exhaust leaks around the o2 sensor that's on the Y pipe. I've seen this DTC setting to a leaky manifold to y-pipe gasket and air getting into the exhaust stream and causing faulty readings. The gasket is fairly inexpensive from the dealer, I would try to replace it first.
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post #10 of 10 (permalink) Old 05-07-2016, 09:02 PM
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Typically 430 needs more than one drive cycle to set. My guess is that the cats were iffy and changing the alternator changed the system voltage enough to push it over the measurement threshold
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