1999 lincoln town car a computer says evaporative emission system leak detedcted a sm leak .. what does this mean

Location

https://www.google.com/search?q=2006+gmc+canyon+canister+purge+valve+location

The Codes

P0455 GMC Code - Evaporative Emission Control System ...

https://www.engine-codes.com > p0455_gmc
P0455 GMC Code - Evaporative Emission Control System Leak Detected Gross Leak · Possible Causes · How To Fix · Tech Notes ? · Cost to Diagnose · Meaning.

P0442 GMC Code Evaporative Emission Control System Leak ...

https://www.autocodes.com > p0442_gmc
Aug 17, 2017 - The P0442 code means that the control module has detected a small leak in the Evaporative Emission (EVAP). Loose fuel tank filler cap is the ...

The P0455 means Evaporative Emission Control System Leak Detected (gross leak) and the P0446 means Evaporative Emission Control System Vent Control Circuit.
_____________
NEXIQ 125030 usb link

P0442 Evaporative Emission Control System Leak Detected Small Leak
http://engine-codes.com/p0442.html


P0420 Catalyst System Efficiency Below Threshold Bank 1
http://engine-codes.com/p0420.html

Read more: http://engine-codes.com/search_codes.php?var=p0420#ixzz26yDZiDgG

Evaporative Emission System Vent Control Circuit

P0305....Cylinder 5 Misfire Detected

P0442....Evaporative Emission Control System Leak Detected (small leak)

P0455....Evaporative Emission Control System Leak Detected (gross leak)

That is a problem in the evaporative emission control system.
Could be anything causing it
Clogged filter in the charcoal canister
A leak in one of the vacuum lines
The purge valve not working,,,etc.
The best thing is to take it and have it checked out, they might have to do a smoke test to find the problem.
All they do is inject smoke into the system, if there is a leak the smoke will come out of it. All it takes is a pin hole in these emission systems to screw it all up.

P0446 Evaporative Emission System Vent Control Circuit.
The following are descriptions of all Evaporative possible codes:

P0441 Evaporative Emission System Incorrect Purge Flow
P0442 Evaporative Emission System Leak Detected (small leak)
P0443 Evaporative Emission System Purge Control Valve Circuit
P0444 Evaporative Emission System Purge Control Valve Circuit Open
P0445 Evaporative Emission System Purge Control Valve Circuit Shorted
P0446 Evaporative Emission System Vent Control Circuit
P0447 Evaporative Emission System Vent Control Circuit Open
P0448 Evaporative Emission System Vent Control Circuit Shorted
P0449 Evaporative Emission System Vent Valve/Solenoid Circuit
P0450 Evaporative Emission System Pressure Sensor/Switch
P0451 Evaporative Emission System Pressure Sensor/Switch Range/Performance
P0452 Evaporative Emission System Pressure Sensor/Switch Low
P0453 Evaporative Emission System Pressure Sensor/Switch High
P0454 Evaporative Emission System Pressure Sensor/Switch Intermittent
P0455 Evaporative Emission System Leak Detected (large leak)
P0456 Evaporative Emission System Leak Detected (very small leak)
P0457 Evaporative Emission System Leak Detected (fuel cap loose/off)
P0458 Evaporative Emission System Purge Control Valve Circuit Low
P0459 Evaporative Emission System Purge Control Valve Circuit High
---
At least the cap isn't loose for the gas tank.

I would clear the code with an OBD-II Scanner 'erase code' button, and see how long it takes for it to come back.

P1450 = Inability of Evaporative Emission Control System to Bleed Fuel Tank.

This means you have either blockage or a leak in that system. Or possibly your charcoal canister is bad. Do you regularly top off your gas tank? This is usually what makes a charcoal canister fail.

Either the fuel cap, or the evap solenoid on the charcoal canister. I'd start with the fuel cap.

Check your gas cap. If someplace can test it you might luck out. This website advertises manuals and info online. The evaporator cannister is suppose to purify excess fuel vapors. But a system which is not sealed will code an error lamp.