Evap codes revisited
 

I'm hoping some experts can tell me exactly what component may be at fault causing my '09 Aspen to give me the gascap message and 456/457 codes.

Here's exactly what happens...

ONLY after a fill-up, and ONLY after the next 2 colds starts, the gascap message comes on then after a couple run cycles the engine light comes on. What is at fault here? I have a new gascap on it but that's certainly not it.

Right after my last fill-up I got home and disconnected the battery to reset everything. I'm down to 1/4 tank now and no gascap message or engine light.

Is there a sensor to blame for this?

Thanks,
JT

What happens is this.....The same way that your vehicle knows there is an evap system leak, is what is going on here, The difference is that A GASCAP will NOT fix it.

When you shut the car down, A SNAPSHOT of your fuel level is posted in the computer. When You start the car , one of the self tests that is performed is "LARGE EVAP LEAK TEST" which will detect a LARGE leak in the evap system , and Light up the C/E lamp with the appropriate code.

Moving on.... If you were to go to the gas station......You shut the car off, The snapshot is posted,You add gas to the tank, and you start the car. That snapshot is compared to the new fuel level, and the car "KNOWS" he just got gas. If the LARGE LEAK SELF TEST fails, Immediately after Adding fuel, Your computer comes up with the LOGICAL scenario, that you forgot to put the Cap Back ON.....

ESIM....evap system integrity monitor....

On the forward edge of your fuel tank, is the evap canister. there will be a "White rectangular box" on the canister. HE is the one responsible for the leak testing.

Thank you for the reply. I guess I understand how it works.

Can I assume it ONLY performs the large leak test after adding fuel?
Mine only comes on after 2 cold starts.

It's a big pain in the butt if you ask me.

JT

Well....yes and no...

Large leak is performed after every cold start, but there is alot of other criteria to consider, Such as fuel level and ambient temp.
An erratic fuel level sensor would also cause this, but I noticed that you didnt complain about fuel mileage, or an Incorrect fuel gauge. So we push that one aside for now...

Esim failure is common on ALL of the Aspen models ............

MILEAGE...?????? If it is still under 3/36 warranty, by all means ...take it in.

No problem with fuel mileage or the fuel gauge. I guess the pesky ESIM is to blame. It's not under factory warranty but I purchased the "Premium Plus" package (I think that's what it's called) from National Warranty. Hopefully that covers it.

JT

Went out today and got the engine lamp right at startup. No gascap message. That is after using 3/4 of a tank of gas and no codes showing.
This thing is obnoxious.

JT

Filled up a couple days ago. Went through 3/4 of a tank with normal travel. Engine light has been on since last fill up. Yesterday the gas cap message came on out of the blue.

This has to be a faulty sensor.