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Prius Check Engine Light

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Posted by David T. Johnson on January 6, 2009, 4:09 am
I have a 2006 Toyota Prius with about 50K miles.  The check engine light
came on a few days ago after the fuel filler cap was left dangling for
two days after a fillup.  The DTC code from the OBD2 scanner was P0440
for "Gross Evaporative Emissions leak."  I put the gas cap back on and
waited for the check engine light to go out by itself.  It never did.
The prius (unlike some vehicles) does NOT reset that DTC code (and
probably others) even when the source of the fault is no longer present.
  I manually erased the DTC code after two weeks which turned the check
engine light off.  It did not come on again.  It seems to take a day of
operation with the fuel filler cap off before the DTC code is set and
the check engine light comes on but...once it does come on your only
option is to take the car to the dealer or get yourself an OBD2 code
reader to reset it.  If the dealer says you need expensive fuel system
component repairs, get a second opinion as there may be absolutely
nothing wrong.

Happy trails...
Posted with OS/2 Warp 4.52
and Sea Monkey 1.5a

Posted by Michael Pardee on January 6, 2009, 4:18 am

That is roughly my experience; the evap code takes a long time to come in
and a longer time to clear. I'm sure it eventually clears... how long did
you wait? I know ours (2002) stayed on four days or so before I got to it.

Apparently the code is set when the system does an evap check, which may
occur a couple times an hour or a couple times a week depending on the
vehicle. I guess the Prius is toward the longer period. One "pass" is rarely
enough to reset any "check engine" fault.


Posted by David T. Johnson on January 6, 2009, 4:09 pm
 Michael Pardee wrote:

I left it on for three weeks.  It did not clear.  I read online that the
Prius would clear that code itself so I waited expectantly for the
'check engine' light to go out all by itself.  After three weeks I got
disgusted and reset it while thinking that maybe there really WAS a leak
somewhere.  Then I waited for the code to set again in the event of a
leak.  There was no leak.  The Prius does NOT reset the P0440 code (and
probably some others) even when the underlying fault (no gas cap in
place) is gone.  Or at least MY Prius doesn't reset that.  I suspect
that the Toyota engineers reason it this way:  Delay setting the code
for several cycles so that if an idiot owner briefly leaves the gas cap
off, it won't set the code.  If the code does set, though, do not reset
it until the system has been inspected to find the fault.  Toyota
apparently never imagined that anyone could drive around for more than a
day with the gas cap off.

Posted with OS/2 Warp 4.52
and Sea Monkey 1.5a

Posted by Tomes on January 7, 2009, 1:41 am
 "David T. Johnson"...

There are a few other things that one can do to reset codes without having a
scanner.  One is to go to a place like AutoZone who will read the codes for
you [ostensibly in the hopes that you will buy the part to fix it] and then
let you push the button to clear the codes.

Another is to pull the fuse that resets the computer.  A third is to
disconnect the battery for about a half hour [same as pulling the fuse as
far as the computer is concerned].  The second and third ways I have not
tried in a Prius, but they have worked in my Sienna.  I would have to go
look up what fuse it is [something like the EMT fuse or something (???)],
but that is not happening right now.

Hope this helps,

Posted by Michael Pardee on January 7, 2009, 3:25 am
Worth noting: most ECUs are learning devices. Killing the power to them, by
pulling a fuse or disconnecting the battery, requires it to relearn
everything it knew. That is not always a bad thing, though.


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