What are the probable causes for DTCs P0172, P0446, and P0455?

Could be fuel line leak or evaporative.#455.

Here's a link to code P 0133. P0133 OBD II Trouble Code Here's a link to code P0455. P0455 OBD II Trouble Code

code p 0440 refers to EVAP system--system malfunction==causes --hose connections --intake leak---EVAP canister purge valve
code p 0441 refers to EVAPO system --incorect flow detected ====causes --hose connections ---intake leak---EVAP canister purge valve
code p 0446 refers to EVAP system---vent control--circuit malfunction====causes wiring---EVAP canister purge valve ---ecm
replace the purge valve
as to where it is , the location will be in the workshop manual or have a shop point it out to you.

code p0446 refers to evaporative emission (EVAP) system-vent control-circuit malfunction===causes --wiring--EVAP canister purge valve--ECM
code p0455 refers to EVAP system-large leak detected===causes --hose connections--intake leak--EVAP canister---EVap canister purge valve
code p0172 refers to system too rich, bank 1===causes intake blocked---EVAP canister purge valve--fuel pressure ---EGR system---injector/s ---ECM
because the EVAP purge valve appears in all codes I would be inclined to change that unit first the run the fault codes again

Smoke testing for codes P0171 P0174 - YouTube

? 5:48
www.youtube.com/watch?v=kZsqEfP-5zM
Jan 18, 2011 - Uploaded by realfixesrealfast Smoke testing for codes P0171 P0174 .... I have a 1995 ford mustang gt 5.0 and it keeps having a Fault code 176 pop up. ....Ford Explorer P0174 code intake air leak check engine light by froggy - Duration: 16:11. by froggy ...

All the P0300 codes are engine miss codes. The P0455 is a catalyst inefficiency code and the P0172 code is a rich mixture code. All of these could be caused by faulty oxygen sensors. What kind of car, engine size and mileage is it?

P0449 - Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction

P0455 - Evaporative Emission Control System Leak Detected (no purge flow or large leak)

Both are refer at EVAP system; other EVAP DTCs: P0440 - P0441 - P0442 - P0443 - P0446 - P0453 - P0455 - P0456

This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms: You likely won't notice any drivability problems.
Causes: most likely means one or more of the following has happened:
A loose or improperly affixed gas cap
A non-conforming gas cap (i.e. not factory/original brand)
Other leak or damaged piece in EVAP system

Possible Solutions: the most common repair is to:
Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
Otherwise, replace the gas cap, and/or
Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary


Hope helps.

Code P0172 relates to the engine running too lean.
Code P0455 indicates that a leak has been detected in the Evaporative Emission Control System.

P0455 is most often caused by a a problem with the gas cap. It is either incorrectly installed, damaged or just worn out. Other possible causes are a leak in the EVAP system caused by damage or a loose vacuum line.
To solve this first check your gas cap for any damage or wear. For the EVAP system check under the hood. Listen for any vacuum leaks or for the odor of fuel. Check all the vacuum tubes and hoses for breaks in the line. If you find any repair or replace them.

The cause of P0172 is usually associated with a bad O2 sensor but this is not always the case. The causes could be a vacuum leak, an issue with the Mass Air Flow sensor (MAF) or some type of restriction with the fuel system.
The solutions are to inspect the inspect all vacuum and PCV hoses (which you have already done). Inspect and clean the MAF sensor. I am unsure what type engine you have but this will be located somewhere between the intake manifold, possibly on the large black air intake tube.
Finally check the fuel system for leaks. Also the fuel pressure should be checked. You should also run a good quality fuel injector cleaner through a couple fill ups.
After you have done all the simple tasks, (inspecting the gas cap and inspecting the vacuum line and hose on the EVAP system replacing if needed and the fuel injector cleaner. Get your codes reset and wait to see if they come back. If so I think your next step is to replace the O2 sensor. If this still does not solve the problem you will most likely need a complete engine analysis before you can continue.
If you get to that point you should re-post here with the results of the analysis before spend a large sum of money.
I hope this helps and good luck.

P0446 - Vent Control of the Evap System. This Evaporative Emissions System is very complicated. These particular DTCs (Diagnostic Trouble Codes) can be caused by MORE than they tell you. Three MAJOR components in the system can cause this P0446. 1. Charcoal Canister, 2. Charcoal Canister Filter, 3. Canister Close Valve, 4. Fuel Tank Pressure Sensor, 5. Purge Control Solenoid Valve, 6, Wiring and/or connector/connections between them and the ECU. If you wish to trust the computer's diagnostics, then replace the canister close valve (after you have inspected the Evap Charcoal Canister's air filter and find no problems with restrictions of air flow). If the problem comes back, check the Purge Control Solenoid Valve and the operation of the Fuel Tank Pressure sensor - either one of those components, if malfunctioning, can cause a P0446.