trouble codes: P0440 vs P0455
 

(04 Cavalier) I'm getting P0455. New gas cap didn't help, & I didn't
see anything flagrant on visual inspection.

Reading about the EVAP codes, it seems that P0455 means a "large leak",
while P0440 means the self-test can't reach its target tank vacuum ...
which I'd think would also imply a 'large leak'.

Is there some useful difference between these codes?

Thanks

trouble codes: P0440 vs P0455
 

On 8/27/2013 7:38 AM, George wrote:
> (04 Cavalier) I'm getting P0455. New gas cap didn't help, & I didn't
> see anything flagrant on visual inspection.
>
> Reading about the EVAP codes, it seems that P0455 means a "large leak",
> while P0440 means the self-test can't reach its target tank vacuum ...
> which I'd think would also imply a 'large leak'.
>
> Is there some useful difference between these codes?
>
> Thanks
>
My understanding is that they're pretty much the same thing, just the
threshold for triggering the P0455 is greater than that for triggering
the P0440. IOW you can have a P0440 without a P0455 if you have a small
leak but not the other way 'round.

nate

trouble codes: P0440 vs P0455
 

George wrote:
> (04 Cavalier) I'm getting P0455. New gas cap didn't help, & I didn't
> see anything flagrant on visual inspection.
>
> Reading about the EVAP codes, it seems that P0455 means a "large leak",
> while P0440 means the self-test can't reach its target tank vacuum ...
> which I'd think would also imply a 'large leak'.
>
> Is there some useful difference between these codes?
>
> Thanks

Like many codes there are multiple codes that can occur to point to
individual problems.

P0455 in conjunction with something like P0300 could point you toward a
vacuum leak around the engine, like the line to the tank.

P0455 in conjunction with with P0440 means that the front systems are
working (the EVAP & purge controls are working) but that there is a leak
in the tank or lines that is causing the problem.

That is where having people post ALL the codes they get can make you
look at entirely different areas than a single code.
It is also why you can't use the codes as a direct pointer to a part for
the most part.


In the case of the P0455 an EVAP smoke machine can cut the time hunting
by hours!

Check out TSB
04-06-04-025A Check Engine Light, Malfunction Indicator Lamp On, DTC
P0455 Set (Replace Fuel Tank Pressure Sensor)
as well


--
Steve W.