Evap operational question (vacuum valve)

Rudy Technician Montebello, California Posted   Latest  
Resolved
Emissions
2001 Toyota Tacoma 3.4L (N 5VZ-FE) 4-spd (A340E)

I replaced the vapor pressure sensor for being stuck.

After the repairs I let the vehicle run for a few minutes while attending something else. I came back and double checked my connections before closing the hood and I accidentally touched the vacuum switching valve for the VPS and it was burning hot!! Hmmmm I dont think that is correct.

I pulled out my DMM and back probed the VSV while the vehicle was running:

pin 1 (rd/wht) had source voltage

pin 2(grn/blk) had constant ground

Now if Im not mistaken, pin 2 is the ground control side from the PCM,agreed? (see diagram) 

If this is correct, then am I correct in assuming that there should not be a constant ground there? Should the PCM only ground that side under certain conditions?

If I understand the evap operation of this vehicle correctly,the VSV for the vapor pressure sensor is used for leak testing,is that correct? Bad PCM?

TIA.

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Pedro Owner/Technician
Cayey, Puerto Rico
Pedro Default
 

IK6?

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Rudy Technician
Montebello, California
Rudy Default
 

Huh?

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Richard Instructor
Palmetto, Florida
Richard Default
 

on an early Toyota evap system the vsv is switched on or off to allow the vapor pressure sensor to see pressures on each side of the evap system (canister side and tank side) it would be normal during an evap monitor for it to be held on for an extended period of time. You can use just about any decent scan tool‘s bi-directional commands to see if the pcm has the ability to switch the vsv on/off.

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Rudy Technician
Montebello, California
Rudy Default
 

Ok so it may come on for an extended period,but the VSV measures 185 F after the vehicle has been idling for 15 mins.(200 F after 20 mins!!) It is sitting on the left fender away from any heat source. The PCM never ungrounds it, so Im thinking it may be a problem. (Or maybe thats normal. Im not really sure,doesn't seem like it would be normal,but its not something I really noticed.) My scan…

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Ray Diagnostician
North York, Ontario
Ray Default
 

What is the amp draw of the VSV?

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Rudy Technician
Montebello, California
Rudy Default
 

250ish mA

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Ray Diagnostician
North York, Ontario
Ray Default
   

Is the PCM grounding the VSV at KOEO. With the key off, connect a powered test light to the G/B wire, near the VSV. Is the test light lit?

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Rudy Technician
Montebello, California
Rudy Default
 

It'll have to wait til Monday for the test light. However, the PCM is NOT grounding the VSV KOEO, I did check that before I went home.

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James Owner/Technician
Pike, Pennsylvania
James Default
 

I believe Pedro was referring to the connector 'IK6' between the sensor and ECU as a possible issue and to disconnect the connector to see if the full time ground disappears from one side or the other.

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Pedro Owner/Technician
Cayey, Puerto Rico
Pedro Default
 

Thanks, buddy!✌📉📈📊💻🚘

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Rudy Technician
Montebello, California
Rudy Update
 

Ok well, I went well over the initial 1 hour time we got and actually delt with the original check engine light and stumbled into another problem. Unfortunately I cannot go further unless the customer approves more time. Ill update this post if he does (Ray I did mange to attach my test light(which itself is a 220mA draw) and there is no ground with key off)

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

Off-topic vato, but have you found a 220mA bulb for standard test lights or is that a self-made test lamp? My pack of OTC bulbs are 150mA. Not super important - just curious. I also have one test light with the "new" 50mA bulb that GM specifies (starting like ten years ago). And my big-boy test lamp is 3.6 A :-) Aloha,

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Rudy Technician
Montebello, California
Rudy Default
 

Honestly I never bothered measuring test lamp draw until I read about it like 2 years ago on iATN. The one I have now is my only one. The others have been lost or tossed through out the years. (I also have a PP3 which I think measured like .25mA)

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

K Thanks. I use my test lights more than my scan tools out here. All the dang no-start tow-ins. One is for starters, one is for fuel pumps.

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Rudy Technician
Montebello, California
Rudy Update
   

Ok back on it. I decide to use my Autel and found it has more(relevant ) data than my Snappy. Namely,it shows the commanded state of all 3 VSVs for the evap system. In this case, the PCM was actively commanding the VSV for the pressure sensor on. I let the truck idle for 30 mins and then drove it for another 20 mins afterwards(with scanner and Fluke 233 connected) and the PCM never commanded…

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Rick Educator
Concord, California
Rick Default
 

Rudy, Here is part of a document I wrote on Toyota EVAP systems: Non-Intrusive System Operation The non-intrusive system is designed so the PCM can monitor charcoal canister side or fuel tank side pressure, but it cannot measure both sides at the same time. The PCM tests for leaks by measuring EVAP system pressure in the lines, charcoal canister, and fuel tank. The vapor pressure sensor vacuum…

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Rudy Technician
Montebello, California
Rudy Default
 

Thank you Rick, I believe I do have a proper understanding of how this system works. However I am missing a piece of information which I cannot find: What input(s) does the ECM look to,in order to determine when to turn the VSV off and on? (In my case it turns on the VSV when the vehicle is started and does not turn it off, even after an hour of drving/idling) In addition to the above, the…

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Rick Educator
Concord, California
Rick Default
 

Rudy, The only time that VSV Solenoid should be energized is when the monitor is running. The VSP reads either Canister side vacuum or Tank side pressure. At that point, the PCM grounds the circuits and reads Tank Pressure. Once the Monitor testing is done it should deenergize again. This should only take 30-60 seconds. Based on your testng and that the Purge and VSV are always energized it…

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Rudy Technician
Montebello, California
Rudy Resolution
   

Welp. I was wrong. Way wrong. Super wrong. The condition I have described above is apparently normal operating condition. Burning hot valve and all!! I got a replacement PCM in today(used) and the vehicle behaves in exactly the same manner. VSV valve gets very hot, is never commanded "off" in the data PID and the purge valve purges constantly,even if it is commanded "off" in the data…

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