Thursday, August 22, 2013

Nissan Altima P1491 Check/Replace the Vacuum Cut Valve Bypass Valve on a 1998, 1999, 2000, 2001


Description:
This post describes one of the diagnosis steps for the P1491 codes on a 1999 Nissan Altima. Specifically the testing and replacement of the vacuum cut valve bypass valve. This applies to all second generation Nissan Altimas which are 1998, 1999, 2000, 2001.

The vacuum cut bypass valve is installed in parallel with the vacuum cut valve on the EVAP purge line that runs between the fuel tank and the charcoal canister.

Nissan EVAP Diagram

The purpose of the vacuum cut valve (white part in the pictures below) is to prevent the intake manifold vacuum from being applied to the fuel tank. The vacuum cut valve bypass valve is energized (opened) for diagnostic purposes to bypass the vacuum cut valve to apply the intake manifold vacuum to the fuel tank. This verifies the intake manifold vacuum.

Location:
The vacuum cut valve bypass valve (what a mouthful!) is located just inside of the passenger side rear tire, next to the gas tank and spare tire compartment. You can locate it by looking for the charcoal canister which is a large, black square box on the drivers side of the gas tank, and then following one of the lines until you see a white cylinder with four tubes coming out of it. That is the vacuum cut valve. The vacuum cut valve bypass valve is located on the same metal bracket as the vacuum cut valve. Here is a picture of the bracket/valve assembly after it has been removed.


In order to check the vacuum cut valve bypass valve we need to first remove the assembly.

Removal: 
Make sure your car is off, disconnect the battery and block the tires.

1. Slide the two hose clips away from the white vacuum cut valve and carefully remove the hose from the vacuum cut valve tubes. Twisting sometimes helps.


2. Remove the two 10mm bolts that hold the metal bracket assembly to the chasis. Be careful to no strip these bolts. I had one of mine strip and had to use mechanic wire to fasten the bracket in place. I suggest using PB Blaster well in advance of doing the actual removal and letting it soak. 


3. I like to save the electrical connector for last so that you can have the assembly dangling low for easy access. Push the green tab "in" and pull "out" on the exterior. You should be able to hear/feel a click when you get the green piece pushed in far enough.


4. Unbolt the vacuum cut bypass valve in order to diagnose it using the below steps.

Diagnosis:

Perform the exact same battery energizing test that I used on the similar EVAP purge solenoid valve. If you don't hear the solenoid valve click/move (or air passage) when power is applied then yours is bad!


For additional diagnosis steps for the vacuum cut valve go here.

Replacement:
I was only able to find a replacement over at Quality Resale Auto Parts (the website is a bit sketchy but they shipped the correct part, as described, and quickly) for $38 shipped. It's hard to beat that. Here's a comparison shot of the old vs. new solenoids. Why don't they encase/seal these parts better? Darn you northeast salt!


The steps to replace the assembly is just the reverse of the removal. 

Hopefully this write-up was helpful. Please feel free to comment about successes, or suggestions for improvements!

11 comments:

  1. Thanks for writing this -- I'm waiting for the penetrating oil to soak through the rust on my son's 2000 Altima.

    For us Yanks, in case others find this on a Web search like I did, the valve is on the left side of the vehicle.

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    1. You're welcome! I'm glad you found it useful. Feel free to report back with any tips/tricks/suggestions after your fix!

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  2. 1999 Altima GXE. I get P1491 only during long trips, say, 50 miles of highway driving. After I clear the code, if I'm doing my normal 5-10 mile daily commute for months on end, I don't get P1491. And it seems to have no effect on driveability. I'm wondering if I should tackle this job at all. Thanks for the helpful write-up.

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    1. So, I went ahead and replaced the valve. Wound up snapping one of the bracket bolts. My old valve looked about as corroded as yours. Took the Altima for a long drive (about 80 miles), and P1491 is...still there. Service Engine Soon light came on at around 65 miles, as usual. Seems like nothing's changed.

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    2. Hey Joe,

      Sorry to hear that it didn't go as smooth as planned and that it didn't solve your code. Did you check your valve via the battery method to determine it was in fact bad before or after replacing it? It's possible that the valve wasn't really your problem, or that there is more than one problem. If you haven't thrown your old one away I would definitely check it. Good luck and keep us posted.

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  3. I did test the old VCVBPV only recently (http://tinyurl.com/oa2vky2), and it seems to still function. I suppose I could try to hunt down other possible causes like clogged or leaky vacuum hoses, but I have bigger fish to fry on this car right now.

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  4. Hi,
    Thanks for the great details, i have bookmarked your blog for the future references.

    We leading manufacturers of Syntho Glass, Solenoid Valve, Pumps, Blowers, etc

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  5. i have a98 altima .but my problem is like PO 171 and i cant fuel my car complete .because back up after half tank.

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  6. would the p1491 code cause the car to fail the smog check?

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    1. Typically they won't even do the emissions test (what I believe you mean by smog check) when there's a check engine code. They might have done the safety inspection and allowed you to pass that, but you would fail (no test) the emissions portion.

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  7. Thank you, Chad! Your post was very helpful, especially when I had to orient the replacement parts correctly. My bracket was completely rusted so I had to engineer a replacement bracket to hold the solenoid and valve. No problem!

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