Purge Valve Test

Does anyone know the correct voltage and polarity to put on the pins of the purge valve to test it?

My check engine codes are (P0) 441, 442 & 446. My gas cap looks good. I pulled the tank hose off of the purge valve, located behind the fuse box under the hood, and found that the valve does not open and close when the engine is warmed and running. The tank never has a rush of air when the gas cap is opened. The system is no longer pulling vacuum on the tank. I would like to pull the valve and bench test it by applying power to the 2 pins, but I need to know the correct voltage and polarity. Thanks!

 

just what year are you working on?

A simple matter to test at the Plug on the Harness one pin will have continuity to ground!! Making the Other positive!

 

I'm working on a 2004 Tacoma, 5 lug single cab. I don't know if it's switched power, switched ground, or Pulse Width Modulated power. My goal in testing the switch is to determine if it's defective, or if I need to look at the wiring or ECM.

 

Do you have a digital copy of the FSM? https://www.tacomaworld.com/threads...tory-service-manual.5696/page-9#post-29401650 It should have the complete wiring diagrams, and steps to troubleshoot the various components. Navigating it isn't the easiest in the world, but it's all in there.

 

Couldn’t you just pull the inlet hose off the vsv after engine reaches operating temperature to check for vacuum?

 

I have done that test. The valve fails the test, and the system never pulls vacuum on the fuel tank either. I would like to test the valve to verify the reason is the valve, not the vehicle wiring or ECM.

I want to thank Andy01DblCabTacoma for a good link to the manual. I'm working my way through that now -- there are a lot of pdf files, all with short and cryptic names! 020ecs2r seems to be a good start. The easy to read pictures from TnShooter seem to cut right to the chase. Thank you, that also is helpful.

 

Start with the index.html file- it's links to each of the pdf files/pages.

 

With the engine idling (and the electrical connector removed), if there is vacuum present on the canister side of the purge valve then it is bad and should be replaced. No need for any pin-point testing

But i can understand if you're curious and want to verify pcm control.. a good time to check would be a couple minutes after a cold start. The pcm likes to duty-cycle the valve at this time..

 

My fault is the opposite. There is NEVER vacuum when engine is running. There is no rush of air when opening the gas cap. The valve is staying closed. That could be the valve, the wiring, or the ECM (I think).

 

Or a leak somewhere like a split rubber line. If the system is open to atmosphere it will never be able to build vacuum either

Can you get your hands on a smoke tester?

 

It is called the "VSV (Pressure Switching Valve)." The Toyota part number is

$74 25860-75230 Vapor Canister Purge Solenoid

25860-75230. It also has a couple of other names in different places ("VSV for EVAP" or "PMW Vacuum Switching Valve"), making it a bit of a PITA to follow in the book. The valve is located in the engine compartment behind the fuse box. The valve is powered by the EFI Relay.

I have disconnected the charcoal canister line from that valve. The other line on the valve is a vacuum line to the throttle body below the throttle blade. There is no vacuum and the line between this valve and the engine appears to be intact. That is why I'm confident the valve is not opening.

I'd just throw a new VSV for EVAP at it but that part is around $100. I would like to know if there is a test for the control circuit. I've got to put the Tacoma to work tomorrow so I'm not going to get back into this until later this week. The failure is not causing a lean condition error code and the truck is perfectly drivable. I don't have to pass smog, but prefer to keep everything working correctly and the check engine light off.

 

Not trying to bug you but you need to look for leaks before condemning a part. The only way the pcm knows if the purge valve is working is to see vacuum build up in the evap system when it commands the valve open.. and see the vacuum drop off when it opens the valve.

There's also a vent valve at the canister that could be leaking too.

The point is any leak in the system will keep it from being able to suck a vacuum so it will code for the purge circuit, but the purge valve can be working fine the whole time

P0441 doesnt necessarily mean the purge isnt working, it's computer speak for "i commanded the purge to open and I'm not seeing any vacuum building up"

 

An electrical test is easier than chasing at least 3 different vacuum lines from end to end of the vehicle. I found a test on you tube, but it shows a working system. Basically, the VSV valve, under command of the ECU, pulls a controlled vacuum on tank by switching on and off several time a second.

Unable to come up with a test for the vehicle side electronics I went to the auto parts store this morning (after getting X-rays on my wrist, broken when I was hit by a car on my bicycle a month ago) and got a larger vacuum line to fit the vacuum switching valve

$74 25860-75230 Vapor Canister Purge Solenoid

25860-75230. The ohm reading for the valve was correct (33 ohms), but with a vacuum line connected I determined that is is not opening when commanded (no 'click' and no air flow when powered). The fault appears to be the valve.

I am also looking for the molded vacuum hose with Toyota part number 23827-75250. It goes between the VSV and the intake manifold. The 21 year old part in my pickup is oxidized on the outside, and if that hose leaks it would be a challenge for the fuel injection, a fairly large intake leak and lean condition.

This is a really cheap vehicle to drive, and less than $14k new! So far my only non-regular maintenance parts needing replacement have been the clutch switch (bypassed) and this evap valve (going to be replaced). At 72k miles I do not even needed front brake pads yet (dealer says about 1/3 of life left).

 

Sure you can use a scan tool to force a vacuum test in the driveway..

What I'm saying is, of there's a leak in a line somewhere it wont be able to build any vacuum at all. The electrical test will tell you if the system can't build vacuum but it wont be able to tell you why it cant build vacuum.

Thats the beauty of the smoke test machine. Pump smoke into the system and then see if its coming out anywhere.

P0442 is a leak code. The computer has been seeing a drop in vacuum somewhere..

 

I could do a vacuum line test, or I could start with an electrical test. The electrical test is a lot easier than inspecting vacuum lines from one end of the vehicle to the other. I don't have a lift and I have a cast on my left wrist right now. I tested the valve in the garage this afternoon. It does not open when powered. If that valve doesn't open there is no way for the EVAP system to pull a vacuum on the charcoal canister and fuel tank. The fact that I no longer have that rush of air when opening the gas cap aligns with this, but would also align with a vacuum leak. Unless I have experienced 2 failures at once (quite rare) the problem is likely the valve. Testing tells me it doesn't work.

Do you know how to force a vacuum test in the driveway? That's the test I was looking for. I have an inexpensive scan tool and I don't think it offers an option to force any type of system test. As near as I can tell from its instructions all I can do is see codes, see some stored vehicle info, and reset codes.

 

If the system was working normally you could jump power to the vent valve (to close it) and jump power to the purge valve (to open it) and then hookup a vacuum gauge somewhere inline with the engine running to see what you got. But if your purge valve isn't responding to a jumper wire then i guess you could just take the vacuum line off the purge and attach directly to the intake manifold at a vacuum nipple? Thats pretty backyard though..

When a scan tool forces a test it closes the vent, opens the purge and watches for a change in vacuum at the fuel tank pressure sensor. And you've got the data pids on the screen watching commands and the FTP sensor voltage

Im not trying to send you down a rabbit hole.. but that purge valve is expensive. Id hate to see you buy one and then have it not fix the problem. On a 20+ year old truck rubber vacuum lines by the fuel tank and canister get dry, brittle and crack. All it takes is a little crack somewhere and then it sets leak codes and purge and vent functionality codes. The only window into the system the computer has is the FTP (fuel tank pressure) sensor. Thats the only way it knows that any of these components are working. So if you have even a tiny little leak somewhere the FTP sensor voltage will never move off of static/atmospheric pressure so the computer is clueless as to what is actually going on.

Good on you for chasing after your evap fault, even pro mechanics struggle with these systems sometimes. They're very finicky and everything mickey-mouse plastic. Good luck

Get a smoke test machine ..

 

I do have a question. I see these EVAP codes had to be set twice before it triggered the check engine light. If I have the problem fixed will these codes clear themselves after a couple of good freeway drives?

 

If you check the valve for suction when there shouldn't be, the suction may be subtle....
Leave your finger on the valve port for a minute or so to see if it creates a suction.
assuming youre not going the the trouble & throwing a vacuum gauge on it....

 

it is true, I did not use a vacuum gauge. I put a section of new vacuum line on the intake manifold port of the valve, pulled a vacuum with my lungs, then had the valve hanging by that hose off the end of my tongue. With the valve powered for 4 to 5 seconds the valve still held vacuum, evidenced by the fact that it didn't drop off my tongue.