Diagnotic Trouble Shoot Code Problem

[jbaflyer]

I had my check engine light come on the other day. I went by Autozone yesterday and they let me use a scan tool for free. A real great tool I need to get! Anyways the following Codes came back

P0441 1 of 4
P0441 3 of 4
P0446 Evaprative emission control system ventilation circulation 2 of 4
P0446 Evaprative emission control system ventilation circulation 3 of 4

I cannot figure out where to find the codes in this forum or in the garage. Any help would be appreciated. I have an 01 LTD 4x4 with are you ready for this 204,000 miles. Still runs like a champ!

Thanks, Brian

[road_hog]

Have you noticed when you open the gas cap you hear the vacuum in the tank releasing? If you do not hear the vacuum releasing, it can very well be your gas cap is not sealing (try new gas cap) or you have an air leak in your EVAP system.

I had a CEL code p0447 on my 2000 Tundra and a new gas cap cured the problem. The oring on the cap has harden over the years and was not sealing.

If you need more direction on the EVAP system I have some pdf files I can send you to help troubleshoot this.

email: wemeny@cox.net

best regards,

Will

[imjin]

I think I had one of those codes back when I changed my timing belt and had bumped a vacuum hose loose by accident. I remember it was a code that was specific to the Evaporative Emission Control, but I can't remember if it was that same code though.

[Hi Volt]

A faulty/loose gas cap should set a PO440 code.

PO441 referes to incorrect purge flow. Specifically the pressure in the charcoal canister does not drop during a purge cycle. Or during purge cut-off the pressure in the canister is very low compared to atmospheric.

PO446 refers to vent control malfunction. Specifically refers to either or both of two VSV's (vacuum switching valves) are not allowing flow from the fuel tank or charcoal canister and cannot be read by the pressure sensor. The pressure sensor and one VSV are mounted to the top of the charcoal canister, and the other VSV is mounted across on the intake maifold. I have commonly knocked off one of the vacuum lines on the intake mounted VSV before while doing spark plug changes, see if it is that simple. Below is further information.

Both your listed codes have the same possible causes, which are:

- Vacuum hose cracked,blocked or disconnected
- open or short cct in vapour pressure sensor cct. or faulty vapour pressure sensor
- open or short cct. in VSV (vacuum switching valve) circuit for the EVAP, or bad vacuum switching valve.
- open or short cct. in VSV (vacuum switching valve) circuit for the vapour pressure sensor, or bad vacuum switching valve ( 2nd one ).
- cracked charcoal canister ( black box on driver's side near firewall )
- ECM fault

What you are looking for is a problem correctly reading the vacuum purge cycle as opposed to a "gross leak" as caused by a bad gas cap.

The system is functioning but isn't coming up with the right specification of measured flow. I would start by inspecting for loose or damaged vacuum hoses. Then look to make sure all the connectors on the EVAP canister and surrounding solenoid valves are tight. Beyond that there may be some bad solenoid valves, you could do a resistance test on them to see if they are either open circuit of shorted. I don't have a resistance spec. handy, however a very low reading ( less than 5 ohms ) or a high reading ( over 500 ohms) is bad. I would guess a nominal reading to be in the 25 to 50 ohm range. Do not try to do an ohms test back to the ECM or on the pressure sensor, just the VSV solenoids themselves ( these have 2 or 3 hoses each, while the pressure sensor has none, only a connector).