jlawr

The Check Engine and VSC lights came on, and the Cruise and Hold Buttons wouldn't work either! Yipes! My code was P0456 and it turned out to be a bad seal on the gas cap that did all the "damage."
The first time this happened at 1500 miles, I took it in they re-tightened the cap. The second time I took it in, they replaced the gas cap.
It seems even if you tighten the cap and hear it click, the cap can loosen over time and cause the check light to come on again. Insist the dealer replace the seal on the gas cap or give you a new one! It may save you a re-trip to the dealer.

Mike_TX

Thanks for the tip.

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ccds

thanks

good to know

Nospinzone

Hmmmm, does anyone know what's the principle behind that? Does the system have to have a certain vacuum in the tank? Right after you fill the tank, or for any reason happen to remove the gas cap, there would be no vacuum right away. And how does that affect electronic functions like the HOLD feature?

jlawr

Well, it's happenned again. Everything was fine when I drove home and parked the car in the garage last night. I came out this morning and there's the check engine light again!

I haven't been to the dealer yet, but I think it's the same P0456 code.

What can I suggest they fix? It's obviously not the gas cap, and I'm using premium Exxon gasoline. What else could in be?

The car drives fine. The Cruise, Hold Button and VSC features don't work.

Any ideas? Any Lexus ASE Techs out there?

Thanx

Mike_TX

I don't think there's any question about it ... I'd demand a brand new car, a free 100,000 mile extended warranty and a box of chocolates. And since it's probably related to that black interior, I'd get a lighter color this time.

On the more sober side, there's probably either a defective sensor or possibly a tiny leak in the fuel system that's triggering that code. It's just a matter of finding it, which I figure they can do.

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jlawr

Thanks for your advice -- and I like living on the "dark side."

Nospinzone

What Mike, no dozen roses?!

Now I just realized that nobody could answer my questions in post #4. Com'on techs!

Mike_TX

If I'm not mistaken, Spin, the gas tank is actually pressurized, as opposed to operating under a vacuum. And if the fuel system doesn't pressurize, then yes, the check light will come on. It's all about pollution - gasoline vapors escaping into the air and all.

As for it affecting other systems, I think they just have it set up so that several kinds of errors all shut down the same set of systems.

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onepointon

I havent had any Evap. codes on the new LS yet.

You seem to have a malfunction with it, such as a leak or so on. I would take it to the dealer and tell them you want some kind of master tech or shop foreman to work on it. The evap problems are tricky, and require someone with knowledge of the system. A lot of people write it off as the customer leaving the gas cap loose, or an unconnected vacuum line, ect..

My guess about the hold and cruise problems, are the same as Mike TX said. Its a fail safe that the computer goes into when the check engine light is on.

Little tid-bits:

The tank is not pressurized, nor under vacuum. The reason your check engine light was on the next morning is because your vehicle does its evaporative emissions check five hours after the vehicle is shut off. Older models used engine vacuum to check for leaks, but this system (called 'key-off') has its own vacuum pump. While the vehicle is running, there is going to be a slight vacuum to compensate for fuel consumption, but nothing crazy. There is a one-way valve that sucks in fresh air from the vacuum.


Feel free to post up any other questions, or even shoot me a PM. You have the option of having a Lexus Master tech, and even the shop foreman to work on your car. Especially when its a third time come back. They know they need to not have a customer come back so many times for the same problem.

Goodluck, sorry I cant fix it for you.



In 1996, along with OBDII, came the requirement for manufactures to monitor the evaporative emissions (fuel vapors escaping into the atmosphere). Your system is supposed to be sealed tight, and only let air escape through the charcoal canister, where the fuel vapors are trapped. The earlier systems (for lexus anyways), were pretty complicated. They have gotten better, but its still hard to diagnose. I actually just went to a Lexus class that mostly dealt with diagnosing these systems. I won't lie, I used to struggle with Evap cars, bad. Now I am confident I can diagnose any of them within 15-20 minutes.

It really takes the right person to diagnose it.

Nospinzone

Thanks Onepointon, very informative. You are number One with us!

az-dave

onepointon:

Ive just had an issue come up with my car, with the VSC light and the throttle response.

It just started Monday....Randomly my check engine light, VSC Light and VSC OFF lights come on, and within a few seconds the throttle quits responding except for the last 25% of the throttle....some type of safe/limp mode.

I replaced the Throttle Position sensor and it is still doing the same thing...yesterday It did it over and over again, and I drove it home...today, I drove to work with the lights on, but it didnt go into limp mode.

Any ideas? I read some other threads on this issue, and even after the other guys take it to a dealer, and replace the whole throttle body, the problem returns...I just dont want to go down the same path.