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FMARA
New User
Nov 17, 2008, 2:23 PM
Post #1 of 3
(11838 views)
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P1491 Code Nissan Sentra
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I have a 2002 Nissan Sentra 5 speed with 90,000 miles on it. The "Check Engine Soon" light has been on for about a month now. On two ocassions the light will turn off for 10 to 15 minutes. Essentially the light is on most of the time. The light does not seem to affect any of engine's performance, from my opinion. I am hesitant to bring the car to a shop because the problem might be simple enough for me to fix. In the shop, they might give me a song and dance then charge me an arm and a leg of a simple repair. I brought it to Auto Zone and borrowed the OBD II scanner and it gave a P1491 code...Vacuum Cut Valve Bypass Valve. Failed Vacuum Cut Valve Bypass valve. Blocked line. I don't know if this is a big deal to replace and where the part is located on the car. Please advise/help.
Thanks...Fred
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DanD
Veteran
/ Moderator
Nov 30, 2008, 6:13 AM
Post #2 of 3
(11746 views)
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Re: P1491 Code Nissan Sentra
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This deals with the evaporative (EVAP) emissions system; in other words, fuel tank fume containment and purge systems.
The by-pass valve that the code relates too doesn’t necessarily mean that the valve needs replacing. It means that the PCM (computer) has commanded a function and didn’t see the results it was expecting. At which time the code sets and the PCM turns the light on, to notify you of a problem.
The problem could be anything from a disconnected/split vacuum line, poor electrical connection, right to the PCM and have nothing to do with the valve itself?
The test procedure is quite extensive as to not misdiagnose the root problem.
So if you do go to a garage too have this tested and you start to hear what you presume is
a song and dance It's likely not but it is the truth that they need to test the circuit(s).
This code and its test procedure, in the service manual; isn’t as simple as, go and replace this or fix that.
It does take you through a number of very specific tests. These tests take time, a good working knowledge of the system and the technician must also know his/her equipment to perform the tests.
This is what you’re paying for; the actual repair could
be simple enough but its getting there; that is the hard part.
One last note (opinion) that I have on this.
A lot of people feel the same as you and I’m sorry, but that is old school thinking.
I am hesitant to bring the car to a shop because the problem might be simple enough for me to fix
Back in the seventies; when I first got in the trade; the diagnosis of a problem was usually reality easy; it was the repair that took the time. Now it’s the other way around; when dealing with today’s electronics.
Dan.
Canadian "EH"
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Loren Champlain Sr
Veteran
/ Moderator
Dec 1, 2008, 5:12 PM
Post #3 of 3
(11724 views)
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Re: P1491 Code Nissan Sentra
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Dan; Very well said!
Loren
SW Washington
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