Code large air leak (emmission light stays on)

The evaporative (EVAP) emission system is all about controlling fuel vapors. When a leak develops, it allows the vapors to enter the atmosphere which is harmful to the environment. Modern vehicles therefore have been designed with a system to detect when a leak is present. There are several different Diagnostic Trouble Codes (DTCs) than can be set for EVAP leaks including those for very small, small, or gross (large) leaks. The most common gross/large leak is from a loose or damaged fuel cap. Because it's the most common, people often assume that the gas cap is the culprit even though it could be elsewhere in the system. Some vehicles even have a fuel cap indicator light that makes this same assumption. If you have a DTC for an EVAP leak and/or the fuel cap indicator light is on and you've already replaced the gas cap, then an EVAP leak test should be performed to locate the true source of the leak. You can read more about large EVAP leaks and the associated warning indicators here: https://www.yourmechanic.com/article/what-does-the-fuel-cap-warning-light-mean-by-spencer-cates

could be your oxygen sensor or catalytic converter.. You may check for leaks in manifold as well.Mass air sensor could also be at fault.

the code is for coolant leak large. Check coolant level and top off.
check the oil for moisture.
pull the plugs to see if any are steam cleaned.
either one could indicate a bad head gasket or worse damaged head.
Check to see if any new hoses have been added. tighten clamps if needed.
look on engine block for any puddles where coolant could be leaking.
pressure test coolant system and check for leaks.
If you can smell coolant inside the vehicle check the heater core.
lastly have an emissions test run with the radiator cap off and at running temperature. Start vehicle with cap off to avoid spray of hot coolant. This tests head gasket and cyl head for leaks.

what code is it?po440,p0455?If it is one of those codes it means you have a large evap system leak not a vacuum leak by the engine.the evap leak is most likely a inop vent valve or a fuel cap not properly sealing.

computer is seeing a large evap leak. most common cause is gas cap left loose this is why it is throwing up that message. since you have already done that we know there is a leak somewhere else. look underr vehicle and should see a black rectangular box close to gas tank this is the evap canister check the lines hooked to this and just do a visual inspection of hoses see if one has come off. may need to have it checked out we have a machine that hooks into system and pressurizes with "smoke" the smoke leaks out of the problem area and helps diagnose .

Why would you buy a gas cap?
You were told a large leak,diagnose those issues ,by having the EVAP System smoke tested and repaired

it means evap large leak, most likely a loose gas cap or recently loose cap and car has not been run enough to clear the code. could also have a lagre leak in the evap system but start with the cap

The leak in your evap system is very small at .020. It is more than likely a small split in a hose somewhere. The cap is probably ok, we rarely find a bad one. If it is a small split in a hose it will only get larger over time. Here is the factory info on the code. We have found that alot of these leaks are from a small hose on the evap canister under the vehicle, but with out looking at your vehicle it is hard to say. If the leak goes away or is no longer large enough to be detected, your light will go out after a few days. These leaks are emmissions related and will not effect the integrity of the vehicle. I would have it checked and corrected if the light stays on at your convienience.

Symptom List:
P0442-EVAP LEAK MONITOR MEDIUM (0.040) LEAK DETECTED
P0455-EVAP LEAK MONITOR LARGE LEAK DETECTED
P0456-EVAP LEAK MONITOR SMALL (.020) LEAK DETECTED
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P0442-EVAP LEAK MONITOR
MEDIUM (0.040) LEAK DETECTED.
When Monitored and Set Condition:
P0442-EVAP LEAK MONITOR MEDIUM (0.040) LEAK DETECTED
When Monitored: Immediately after a cold start, with battery/ambient temperature
between 40° F and 90° F and coolant temperature within 10° F of battery/ambient.
Set Condition: If there is a leak larger than 0.0409 and smaller than 0.0809 in the
evaporative system.
P0455-EVAP LEAK MONITOR LARGE LEAK DETECTED
When Monitored: Immediately after a cold start, with battery/ambient temperature
between 40° F and 90° F and coolant temperature within 10° F of battery/ambient.
Set Condition: There is a leak larger than 0.0809 in the evaporative system.
P0456-EVAP LEAK MONITOR SMALL (.020) LEAK DETECTED
When Monitored: Immediately after a cold start, with battery/ambient temperature
between 40° F and 90° F and coolant temperature within 10° F of battery/ambient.
Set Condition: There is a leak larger than 0.0209 and smaller than 0.0409 in the
evaporative system.
POSSIBLE CAUSES
LEAK AT GAS CAP
VEHICLE HISTORY AND SERVICE BULLETIN INVESTIGATION
VISUAL AND PHYSICAL INSPECTION
VERIFY EVAPORATIVE EMISSION SYSTEM LEAK
EVAP PURGE SOLENOID OPERATION
INTERMITTENT LDP MONITOR FAILURE
EVAPORATIVE EMISSION LEAK DETECTION
GAS CAP
LDP COMPONENT LEAK

code po455 isis no purge system or large leak, only way to find this is with a smoke machine, most shops will do this for a fee,should not be too expensive range 25-75 dollars

I'm not a mechanic but I've had this problem with a dodge truck and a Saturn. I bought a new gas cap and the problem stopped. It takes awhile after you install the new cap for the emmission control system to clear. Something about air gas mix. I don't know about the Trac problem.