P0441 / 1441 EVAP Emission Canister Purge - keeps coming back!

Abaddon wrote:

The purge solenoid IS normally closed until the PCM commands it on.

P0441 is NO FLOW during purge. Either the purge solenoid is bad, or you have a blockage somewhere. Hope this helps......

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I verified that the Purge Solenoid was commanded by the PCM when the suction side of the valve went to 17 in-Hg two minutes after a cold start.

I can see how a blockage would set DTC P0441 if it was between the Vacuum Switch and the Throttle body, which is the source of the vacuum, but I can't see that if the blockage was between the Vacuum Switch and the Vapor Canister.

Doesn't the system presume "No Purge" when the Vacuum Switch fails to "see" vacuum?  Wouldn't a blockage between the switch and the canister tend to create a vacuum at the switch instead of preventing one from forming there?  

I verified that the V. Switch does switch under vacuum.  It went from about 33 ohms at 0 in-hg to some 350 ohm - 1k ohm at vacuums greater than about 1 in-Hg.  The resistance doesn't increase with increasing vacuum (I don't know, maybe it should) it merely switches from a low resistance instantaneously to a higher one when vacuum is applied to it.

The Purge valve actually runs in Duty Cycles, not on/off. The PCM commands it in 10% increments or so. If were operating normally, or you could command it with a scan tool, you would be able to command these different duty cycles and audibly hear the solenoid clicking fast or slow. I would check to see if the 5 volt reference is there (pink wire), the purple wire is the driver within the PCM that controls the duty (ground). The switch uses a constant 5 volt supply. GM still has issues with their purge solenoids, especially on the Intake mounted G-vans. It's usually the Purge solenoid that goes bad in that case. Unfortunately, without a good scan tool, you won't be able to command the Purge to verify if it's functioning properly over the entire duty cycle.....

If you had a vacuum leak or blockage somewhere else, I would assume that something else would screw up as a result of it. My guess is that the "No Flow" code is being thrown because the PCM isn't seeing proper flow at a given duty cycle....

Abaddon wrote:

The Purge valve actually runs in Duty Cycles, not on/off. The PCM commands it in 10% increments or so. ...My guess is that the "No Flow" code is being thrown because the PCM isn't seeing proper flow at a given duty cycle....

I guess I don't understand how the PCM measures the flow.  I thought it was merely the vacuum switch turning on and off and that's apparently too simplified an explanation.

If the Vacuum Solenoid valve is commanded on in increments of 10% at a time then is proper operation that the vacuum at the Vacuum Switch increase incrementally as well?

Does anyone have a recommendation for a scanner with which I can command the components and come to a proper diagnosis?

Just out of curiosity...have you priced a Purge Valve yet? I say just buy it and replace it if it's cheap. Diagnosing an EVAP system usually requires tools that some shops don't even have (like a smoke/nitrogen machine). I feel that you might diagnose until you're blue in the face.

I can say that 8 times out of 10, a car with a "No Flow During Purge" code has a bad purge valve. Only in the rare cases do we need to pull out the smoke machine and find the leak.

Are you sure you're looking at the Purge Valve or the Vacuum Switch? There's 1 of each on your car. If you're simply looking at vacuum on the switch itself, it appears that yours is more than likely working. It's the actual Purge Valve (duty cycled solenoid) that you won't be able to diagnose without a scanner.

Here is the schematic....



The vacuum switch is commanded on with the Purge Valve. I assume this is to allow flow. I'm not all that familiar with the '96 vacuum system. My '98 doesn't have a vacuum switch. So, if the Vacuum Switch is working (which you've verified), you need to locate the Purge Valve and check its operation when the switch is working. I'd wait until it shows vacuum (like you checked before), and then feel and listen to the Purge Valve at that time. It should audibly click quite fast. Follow the plastic EVAP lines to find it. One of them ends at the Purge Valve. I want to say it's on the backside of the engine above the valve cover? Maybe someone else can verify this. But, once again, you can't command it through the duty cycles, so actually diagnosing it is impossible I suppose.

All those parts I believe are available from Rockauto for reasonably low prices. Just out of principle I like to figure out what's wrong before I just start replacing parts out of desperation - which I'm starting to feel. The car still runs great but I don't like staring at an SES light all the time.

I'm also reluctant to take the car into a shop to get sold muffler bearings. Not that they could get away with that.

I'll check the solenoid to see if I hear it clicking when it's on. I don't think there is a seperate Purge Valve on the '96 excepting that valve that the Purge Solenoid is connected to which allows vacuum to be routed to the Vacuum Switch. Thanks.

There is a Purge Valve, and a Purge Vacuum Switch. The schematic I posted is right off of my GM Service Information at work. It's there, somewhere. And, if you read the info above, it specifically states the two in the diagnostic process.
I totally understand the need to KNOW, and figure out what's wrong. But again, EVAP isn't something you can check without a diagnostic tool to help. You can rule out things by visualization (cracks, breaks, vacuum checks), but without the ability to command things on and off (EVAP Vent Valve, Purge Valve), you can't always find the problem.

You don't sound like you could be sold "muffler bearings" or a "blinker fluid" change because you already know where the problem lies. So maybe do some research and find reputable shop in your area if you can't find the problem.

If I lived near you, I'd help. I'm only trying to inform you, that's all.

I appreciate the help. Any recommendation of a scan tool I can use to command some of these components? I borrowed one from O'Reilly's to read the P0441 code.

I don't think there are any cheap scan tools that take command of the PCM and allow you to control things. You'd have to spend at least $1000 to get close.....even the $400-$500 scanners only have the ability to read the vehicle, and some can record data, but not command stuff.

Abaddon wrote:

I don't think there are any cheap scan tools that take command of the PCM and allow you to control things. You'd have to spend at least $1000 to get close.....even the $400-$500 scanners only have the ability to read the vehicle, and some can record data, but not command stuff.

You can search craigslist and eBay for a "GM Tech II" tool, it's a 2-way factory service device.

You should try asking one or more local GM dealers (telephone the service dept) if they will do the diagnosis for you for say 1/2 hour shop time charge.

OK - I solved my P0441 DTC (No flow during purge) problem.  It was a bad Vacuum Switch.

I was under the gun to solve the problem since my registration needs renewal by the end of the month and an emission test is required before they'll let me pay my money.  A "check engine light" is an automatic fail.

Instead of paying $120 shop time at the local dealership to get it diagnosed, I decided to buy a new Purge Solenoid and Vacuum Switch from Rockauto since I was pretty sure it was one or the other that was bad.  I knew that the Purge Solenoid operated but I didn't know if it operated "correctly" - that is, whether it turned on at the correct rate or whatever.

 The old switch when I first tested it back in July or so, had about 350 ohms under vacuum and 0 ohms at ambient pressure. I tested the new vacuum switch to see what sort of resistance it had when vacuum was applied and it went to an "open" or infinite resistance.  So, on a ' 96 at least, the switch is supposed to be normally "closed" (0 ohms resistance) and then "open" (infinite ohms resistance) under vacuum That's what I didn't know before.

Here is my set up to test the switch operation:



The image shows that at about 7 inHg vacuum the old switch is still closed (0 ohms resistance).  The meter should show infinite resistance (so the switch in the picture is bad).

I thought I would let the DTC clear itself which it's supposed to do after three successful purges to find how long it would take.  After having 4 key-starts which included 2 thirty mile trips and 2 short stops/starts at stores after work the DTC had still not cleared.  The next day, after the 5th start and about 2 1/2 miles of driving, the code finally cleared.

Some observations:  I tapped both the old Vacuum Switch and the Purge Solenoid ports on a firm surface which I'd covered with white paper.  I saw no carbon particles which would indicate a failing charcoal canister.

While trying to diagnose this problem, I connected my hand vacuum pump to the gas vapor line in the engine compartment which leads directly to the charcoal canister and could not get the gauge on the pump to read any vacuum at all. I wondered if there might be an air leak in that line since their was no resistance to vapor flow using the pump. If there was a leak in that line that prevented a vacuum from being sensed by the vacuum switch then the DTC would have been set even if the vacuum switch were good.  So if there is a leak in that line (which I don't know because I was too lazy to get under the car to check), it isn't large enough in my car to prevent the vacuum switch from operating.

I hope some of you find this useful information.

Very useful! I'm trying to help a friend with a '98 Park Ave and a P0440 - we did the gas cap because it's seal was obviously bad, and took some sandpaper to the sealing surface on the filler neck because it was rusty, but still can't lick the P0440. I'm not sure what to do next - I was thinking of sending her to a garage that could smoke test it.

Abaddon said on a previous page that his ' 98 didn't have a vacuum switch and my '96 Service manual doesn't list a P0440 code so I think the '98 Park Avenue has a different system than my '96.

When I looked up the P0440 code on the net, there was no mention of a Vacuum Switch failure as a possible cause.

Apparently, the P0440 code is the '98 systems equivalent of the '96 systems P0441 "No flow during purge".

I can say that on a previous emissons test, my gas cap failed the pressure test and they made me buy a new one.  The old one looked just fine.  So I do know that the gas caps can fail. Could that set the P0440 code?

This is what came up on the net (which is 100% accurate, studies show):

P0440 EVAP System No Flow During Purge Possible Causes Setting Conditions
•Charcoal canister is loaded with fuel or moisture
•Fuel filler cap is loose, cross-threaded, damaged or wrong part
•Fuel tank, fuel filler neck or fuel sending unit 'O' ring is leaking
•Fuel tank pressure sensor is damaged, disconnected or it failed
•Fuel tank vapor line(s) is clogged, damaged or disconnected
•Purge valve vapor line is clogged, damaged, or disconnected
•Purge or vent solenoid power circuit is open (check the fuse)
•PCM has failed

If I had the '98 system I would check for the "clicking" noise that Abaddon mentions here:

Abaddon wrote:

The Purge valve actually runs in Duty Cycles, not on/off. The PCM commands it in 10% increments or so. If were operating normally, or you could command it with a scan tool, you would be able to command these different duty cycles and audibly hear the solenoid clicking fast or slow. I would check to see if the 5 volt reference is there (pink wire), the purple wire is the driver within the PCM that controls the duty (ground). The switch uses a constant 5 volt supply. GM still has issues with their purge solenoids, especially on the Intake mounted G-vans. It's usually the Purge solenoid that goes bad in that case. Unfortunately, without a good scan tool, you won't be able to command the Purge to verify if it's functioning properly over the entire duty cycle.....

If you had a vacuum leak or blockage somewhere else, I would assume that something else would screw up as a result of it. My guess is that the "No Flow" code is being thrown because the PCM isn't seeing proper flow at a given duty cycle....

Thanks. The next thing I'll have to check is the fuel sending unit area - maybe it's rusted through. Although it did have the gas tank replaced a couple years ago (because the sending unit area was all rotted out)

P0440 on the '98 is EVAP System Large Leak Detected. This usually means a fuel cap is leaking, or sometimes the Vent Solenoid gets stuck open. Yes, it can be found with a smoke test, but we usually can figure out the problem by monitoring the Fuel Tank Pressure sensor and manually opening/closing the Vent Valve with a Tech II. I've seen a ton of times where the Vent Valve operated electrically, but the plunger breaks. This is why is throws a P0440 and not an actual Vent Valve code (P0446).

A large leak can come from a broken EVAP line, corroded tank, fuel cap, etc. However, if an EVAP line is broken, you will get an EVAP System Flow During Non-Purge code, which is still
P1441 on the '98.

FYI, P0441 is not activated on the '98's because of the lack of a Vacuum Switch.

Thanks, that wouldn't surprise me if it were the problem. You don't happen to have a procedure to manually test the vent valve? (Apply vacuum, apply voltage, reapply vacuum, etc?)

Is the Vent Valve the same thing as the Purge Solenoid?

deekster_caddy wrote:

Thanks, that wouldn't surprise me if it were the problem. You don't happen to have a procedure to manually test the vent valve? (Apply vacuum, apply voltage, reapply vacuum, etc?)

Is the Vent Valve the same thing as the Purge Solenoid?

The Vent Valve is nothing more than electrical on our car. GM doesn't give me any electrical specifications for it, no. All I do is command it on/off and listen to see if it's working, which really doesn't mean much if the plunger is broke. I use a noid light or a low impedance test light on the connector to see if the PCM is actually commanding it on/off. It's not something easily diagnosed usually. ALL it is, is a vent. That's all it does. It's either on or off. It's not like the Purge Valve that is commanded in duty cycles.

The EVAP Purge Valve is mounted near the rear Valve Cover. Follow the black EVAP lines under the hood, and you'll run right into the Purge Valve.

The Vent Valve is located by the Fuel Tank on the Driver Side I believe. It has a 2 wire connector, and one black EVAP pipe going to it.

great, thanks! You rock!

I did those steps and removed those two pieces little black beads were falling all over the place so this is the start at a not so good sign right?

Johnny5 wrote:

I did those steps and removed those two pieces little black beads were falling all over the place so this is the start at a not so good sign right?

You did _WHICH_ steps, exactly?

The first two.. had to come to work and didnt get to raise up the read and look for that can

deekster_caddy wrote:

Johnny5 wrote:

I did those steps and removed those two pieces little black beads were falling all over the place so this is the start at a not so good sign right?

You did _WHICH_ steps, exactly?

The purge valve which was completely blocked and the switch which was filled to the and ends sounds like a Morocca also the line that hooked to it had some more black beads falling out of it so it seems to be more where that came from is what that is telling me

Getting the 1645 (Vent Solenoid Circuit) and 1655 (Purge Solenoid Circuit). If I'm understanding things correctly, this means that the EVAP solenoid itself is bad, and not a vacuum/wiring issue, right? And, assuming I still understood this thread correctly, it could be why I only see ~4psi of boost @ WOT with the car stuttering anytime I get into boost?

Alright, found a fuse that was blown in the drivers side door panel. That took care of my lack of boost, but the car still sputters. Now I'm not getting any codes either. Could a vacuum line be clogged? Plugs? Help? SES light flashes under hard acceleration.

matt270avian wrote:

SES light flashes under hard acceleration.

Which means you're misfiring. You need to run a scan of the misfire counter to see which cylinder(s) is the culprit.

Abaddon wrote:

matt270avian wrote:

SES light flashes under hard acceleration.

Which means you're misfiring. You need to run a scan of the misfire counter to see which cylinder(s) is the culprit.

Cool, thanks. I'll get on that and see what comes up.

So that means it's basically either a plug/wire or a coil then, right?