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normanahoyt
normanahoyt, ASE Certified Technician
Category: Nissan
Satisfied Customers: 371
Experience:  I am a Nissan trained technician and a foreign car specialist
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Nissan/Datsun Altima GXE: is a vacuum cut valve bypass valve

This answer was rated:

is a vacuum cut valve bypass valve known by any other name

normanahoyt :

Hello, my name is XXXXX XXXXX I am here to assist you

normanahoyt :

Can you fill me in on what you are trying to do/fix?

Customer:

vehicle failed emissions & vacuum cut valve bypass valve code came up

normanahoyt :

Can you tell me what the code number is?

normanahoyt :

There are several vacuum valves and I want to identify the correct part by the code.

Customer:

p1490

normanahoyt :

Thanks...let me look that up.

normanahoyt :

Ok, here is a thread that is one of several that relate to this code. Unfortunately, most of the time the problem is nto the valve itself.

normanahoyt :
































1999 Altima 2.42003 Frontier 2.4
2001 Frontier 2.42003 Xterra 2.4
2002 Frontier 2.4

Customer Concern:

Check Engine Light is on. Vacuum Cut Valve Bypass Valve code P1490. The code comes back within 5 seconds of turning on the key. Has a new Vacuum Cut Valve Bypass Valve and no help. Has battery voltage to the Vacuum Cut Valve Bypass Valve.


Average Reported Mileage:
81599

Tests/Procedures:

1. Go to the computer and ground the Vacuum Cut Valve Bypass Valve on the Pink/Black wire at terminal 120 of the Engine Control Module (ECM) through an ammeter and check the current flow. The resistance reading on the old and new Vacuum Cut Valve Bypass Valve is 32 ohms so as long as the ohmmeter is accurate and using 12 volts and ohms law, look for approximately 0.34 amps.

2. Verify that the computer connections are good.



normanahoyt :

I will give you some info on the valve but you may buy and replace it and still have the problem

Customer:

i considered the harness might be the problem also, but what someone told me was the idle control valve also known as the vacuum cut valve buy pass valve looked ruff & possibly missing a vacuum line

normanahoyt :

Here is a picture of the valve and its location.

Full Size Image

normanahoyt :

The idle air control valve has nothing to do with code P1490. This code is an evaporative emissions code and relates to the circuit that operates the VCV valve that I sent you a picture of (not the clearest...sorry)

normanahoyt :

Here is a picture from my parts supplier:

normanahoyt :

Full Size Image

normanahoyt :

You could replace this first but be aware that there are many instances of burnt wiring as well as damaged ECM's. I have to believe that the source of the problem is in the valve itself but there can be consequential damage in wiring and ECM.

Customer:

i have had problems with the ECM in the passed so thats another possibility but i will start with the code problems first

normanahoyt :

Yes, it is unfortunate but Nissan Altimas have had ECM trouble. I would replace this valve, inspect the wiring to make sure it hasn't melted, clear codes and allow them to return prior to any further action.

Customer:

Alan I appreciate all your help . many thanks & have a good day/night

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