Hi folks,

Early this week got the gas cap warning on the odometer display. Checked cap and replaced it with a newish one from my other jeep, but warning light stayed on.

Few days ago CEL came on with code P0457. Cleared the code but came back right away.

Checked codes again today, now have P0457 and P0456.

Weird thing about the gascap warning is that I can clear it with the tripometer button (which when I searched was the way to clear this code), but it will come back on immediately, even without starting the truck. I thought this code was set by comparing engine vacuum, so I thought it was logical that it shouldn't be set without the engine on, right?

I found another post somewhere that these symptoms can be caused by a wiring or computer problem, but there was no information on what exactly the problem is or how to repair it, other than disconnecting the battery, which I am about to try.

Are there any common causes of evap codes? Going to check under the hood since I found a few XJ owners who had battery acid corrode a vacuum hose, but I don't know if the KK has the same issue.

Also, does anyone have insight into this rumour of an electrical problem that can set these codes without an actual evap problem?

Cheers

Myself and several other have had this exact same issue. I'm just about ready to toss in the towel and say its an ecu problem.

_________________
2012 Jeep Liberty KK 109k miles and stong
4" lift.
Gen 5.5 A-Arms
Maxxis 31x10.50x15
ATS42rle

Both codes are basically the same.
P0456 = Evaporative emission (EVAP) system - very small leak detected. Possible causes; Mechanical fault, hose connection(s), EVAP pressure sensor.
P0457 = Evaporative emission (EVAP) system - leak detected. . Possible causes; (filler cap loose/off) Mechanical fault, hose connection(s), EVAP pressure sensor.

The CEL is a one trip fault, and a 3 good trip auto off.
You can clear the code with a Neg(-) battery disconnect. If there is still a fault it will come back "on" during the next drive.

Vaseline on the filler cap "O" ring sometimes can stop this. Also check for burs on the filler tube top.
If all the hoses and connections look good, I'd think it would be the EVAP pressure sensor at fault.

_________________
07 KA Light Khaki, Manual trany.
2.5" Adjust-A-Strut JBA lift, Euro taillights,
Home made; Front Tilt Hood, Roof Rack, RAM Air, & CAI.
ESP Off Switch
Take a ride on the Trō side!

I found a section of hose that runs back from the bottom of the evap solenoid that was dried up and rotten... probably because it runs right above the exhaust pipe near the firewall. Part of the outer layer came right off in my hand.

I couldn't find a part number or diagram for the hose online, and it looks like a PITA to replace since it runs behind the heat shield under the driver seat.

I was going to try crawling under today to tape it up to see if that fixed the code, but the code went away on its own last night! Guess I'll wait and see if it reappears before I try a fix.

EVAP codes can be fun and require very specialized and expensive tools to properly diagnose.

A high end scanner with bi-directional control(OEM version is best) and a smoke machine are what is needed.

Tjkj, I completely agree. Cheeper alternative is to find a shop that just slaps the sticker on! My shop doesn't do that so im sorta sol.

_________________
2012 Jeep Liberty KK 109k miles and stong
4" lift.
Gen 5.5 A-Arms
Maxxis 31x10.50x15
ATS42rle

I've got at least a year before I need the sticker so not really worried about that... more concerned about the remote start not firing if the code comes back lol.

Just out of curiousity, will a regular old glycol-based Halloween fog machine work for smoking the system?

No,you need a mineral based system that will pressurize the EVAP system and a bi-directional scanner to open/close the vent solenoid and purge solenoid.A bi-directional scanner also can force a EVAP test when any repairs are done to check that the system is working properly.