P1441 Code Gone?

[A1218]

For the past few years I've always had an occasional check light for a P1441 code pertaining to the evap system that would come and go about every other week. Changed several components on the evaporator system: canister, vent valve, gas cap, vacuum cut valve, bypass valve, some hoses in engine bay, and smoke tested the system (ended up changing one line). In the end the code still would always trigger.

However... I changed out my fuel pressure regulator at the end of December 2021, that was spitting fuel into the intake causing a hot start stumble. I overlooked this part when I previously pulled the plenum and lower intake last spring to change fuel injectors. Rookie mistake I guess. While changing the regulator this time around, the EGR valve broke when removing the plenum so I changed that and the pipe going to the exhaust manifold from the EGR.

Its been about a month now and close to 1k miles and the code has not shown up as yet. Is it possible that the P1441 was related to parts I changed?

Just curious here.

[VStar650CL]

The pressure return line runs straight back to the tank from the regulator, and a leaky diaphragm will allow the fuel to gradually drain back into the tank after shutdown. Once the fuel drains back, the leaky regulator diaphragm will act just like a pinhole vacuum leak when the ECM does EONV testing. The engine is always stopped for that, so the leak will show up in EONV testing (which happens an hour or two after shutdown) but not a smoke test unless you give it enough time for the fuel in the regulator to drain.

[A1218]

Okay, so the evap code was essentially related to the leaky FPR?

[VStar650CL]

Yep. Once that line empties out, it becomes a garden variety vacuum leak for the fuel tank.

[chevron9ine]

Thanks for the help, I will try this as well and hopefully it corrects my evap code too. Hoping it was my fuel cap but after a few days the code returned. Same occasional juttery start too.

[A1218]

So after 3 months, the p1441 code decided to make an appearance again today.

Guess the FPR didn't solve that issue even though after changing it the code stayed away for so long. It did however solve the warm restart stumble.

Any ideas on this stubborn code?

In relation to the evap system I have changed and done the following already:
- smoke test(revealed a leaking line)
- gas cap
- Canister with vent valve
- vacuum cut valve and the solenoid next to it
- EVAP canister purge volume control solenoid valve (located under the hood)

There is a evap purge valve (has electrical connector as well) under the hood and purge control valve (only vacuum) as well. These haven't been changed and don't want to unnecessarily.

Could it just be old evap lines throughout the vehicle and from age there is some small leak along the line somewhere.

Not too worried about it as it does not affect engine operation, but seeing the check light irks me.

[VStar650CL]

It's possible for anything that hooks into the system anyplace between the canister and Purge Valve and doesn't cause immediate pressure equalization to cause that code, so there isn't much that's left out. The Purge Control Valve isn't likely (or the sensor) simply because you aren't getting any other codes or performance maladies along with the P1441. The code is specifically for the Vacuum Cut Bypass Valve, but it isn't like the ECM can diagnose the solenoid on the VCBV directly, it's inferring from the behavior of the Evap Pressure Sensor whether the pressures in the tank and canister are equalizing. That means a spider's nest in the bypass tube or a vanishingly small leak near the Pressure Sensor can cause it. Let me explain what all the stuff in your system is doing and maybe it will be clearer. This is from the P1441 diagnostic page in the FSM:

I'll take the valves from the engine back to the tank:
Evap Purge Control Solenoid - This connects to a fixed bleed orifice and is open most of the time when the engine runs. It allows a small amount of purge vacuum to be sucked through the canister.
Evap Purge Volume Solenoid - This provides a variable-size vacuum port controlled by the ECM that will pull more or less vacuum through the canister depending on operating conditions.
Evap Purge Control Valve - This is the "master cutoff" that isolates the whole evap system from the intake manifold when the engine is off. It will close during leak testing (EONV).
Evap Canister Vent Control Valve - This allows atmosphere to enter the canister when purging and cuts it off when the system should be sealed. It will close during leak testing (EONV).
Vacuum Cut Valve - This is simply a 1-way mechanical valve that allows flow from the canister to the tank but not the other way. Its purpose is to prevent engine vacuum from being applied to the fuel tank during normal operation
Vacuum Cut Bypass Valve - This bypasses the 1-way Vacuum Cut and allows flow from the tank to the canister. Its purpose is to allow the tank and canister to be connected while checking for leaks (EONV)

Diagramatically, it works like this. Here's a normal cruise, red is engine vacuum, blue is tank pressure (atmosphere, sort of):

The idea is to suck the trapped fuel fumes in the canister into the intake and burn them up. Now here's what it looks like during EONV testing, which always occurs with the vehicle parked and between 1/4~3/4 tank of fuel. Green is tank pressure, blue is atmosphere (actual):

With the Purge Control and Vent both closed and the Bypass open, the whole system of tank and canister become one sealed unit. So by watching the vacuum change with temperature, the ECM can determine if anything has sprung a leak. The problem is, the only way the ECM can determine if the Bypass works is by watching the pressure equalize between the tank and canister when the other valves are closed and the Bypass opens. If that happens too slowly or not at all, the ECM throws a P1441. But you can see from the layout that any obstruction in the hoses will prevent quick equalization, a tiny leak upstream of the canister can fool the sensor, or a leaky Vacuum Cut can prevent there being enough difference for the sensor to see in the first place. A "backdoor" leak like your fuel regulator that only shows up after the car is parked can also cause a situation of "not enough difference to see". So diag gets complicated.

Hope this helps you.

[A1218]

Thanks for providing that detailed explanation of the system. Yes, it did allow for a clearer understanding.

I think I’ll start with blowing out the lines with compressed air. Any recommendation on where I should start with that?

If that does not work I’ll move onto a smoke test to check further for leaks. Though the system does pressurize as I hear the hiss when I remove gas cap. After resetting the code Tuesday, it came back on today with a full tank of gas.

[VStar650CL]

I think I'd start by replacing the Vacuum Cut Valve and making sure those lines (the VCBV too) are all clear. The VC valve serves to depressurize the tank when it's warmer than the rest of the system and builds pressure, so the fact that you got a code with a full tank makes me suspect the VC may be stuck.

[A1218]

I actually did replace the Vacuum Cut valve and vacuum cut bypass valve with a Dorman brand back in October 2020.

Guess I'll take a look at it again.

[VStar650CL]

The VC valve serves to depressurize the tank when it's warmer than the rest of the system and builds pressure

Sorry, typo. Depressurize the evap canister into the tank.

[A1218]

Since having this problem I have replaced the vacuum cut valve, VCVBV, a new Nissan gas cap, and the evap canister purge control solenoid valve under the hood.

The occasional P1441 still persists. It hasn't come back as yet since resetting the computer after changing the battery a week ago but I know it will again.

I know you previously mentioned that any obstruction in the hoses can possibly cause this issue. So I'm planning on blowing out the lines with an air compressor. I saw a nice write up on NPORA on blowing out the main Evap line going from the canister to the purge volume control valve under the hood. But that does not take care of lines to the VCV and VCVBV.

So I was wondering how do you blow out those lines? From the diagram they go to the tank and I don't want to blow anything going into the tank.

[VStar650CL]

Unless you want to drop the tank and blow them out with both ends loose, there aren't really any options for the hose sections between the tank and VC valves. The rest can be blown out section by section.

[VStar650CL]

I suppose you could pop the gas cap and vacuum them out instead of blowing.