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Nissan Altima 1998 - Check Engine Code P1491: What It Means and Repair Cost

Model: Nissan Altima Fault Code: P1491 Posted: 2007-10-27 15:46

I recently completed an engine test run to address a check engine light on my 1998 Nissan Altima. The diagnostic scan returned code P1491. The shop I visited has never seen this code before, and Nissan's support team was unable to provide a clear explanation. Can anyone clarify what P1491 indicates and estimate the typical repair cost? The P1491 fault code relates to the Vacuum Cut Valve Bypass System in the EVAP (Evaporative Emission Control) system. This component helps regulate vacuum pressure so the engine control module can properly monitor for leaks or malfunctions within the EVAP system, such as small or large leaks. The vacuum cut bypass valve is an electronic solenoid located under the fuel tank, near the rear left side of the vehicle—close to a check valve and associated hoses. Potential failure points include: - The solenoid itself or its wiring - Vacuum hoses (which may be cracked, loose, or clogged) - The vacuum check valve Recommended troubleshooting steps: 1. Test the functionality of the vacuum cut bypass sensor. 2. Inspect all vacuum hoses for damage, looseness, or leaks. 3. Verify that the vacuum check valve is operating correctly—replace if suspected to be faulty. 4. Perform a full EVAP system inspection to ensure proper operation. If you're experiencing this code on your 1998 Nissan Altima, it's important to address the EVAP system thoroughly to prevent further issues or failed emissions tests.

Related fault codes
P1491
Comments (5)
Anonymous 2007-10-28 10:14

P1491 refers to a fault in the Vacuum Cut Valve Bypass component. This is part of the EVAP system and helps regulate vacuum pressure so the engine control module can monitor for leaks or malfunctions.

Anonymous 2007-10-28 16:08

Moved to the P1 (Engine & Emissions) forum for better visibility and community support.

Anonymous 2007-10-29 17:27

Hi! Code P1491 indicates a problem with the Vacuum Cut Valve Bypass system. This component allows vacuum air to bypass the main vacuum cut valve, enabling the engine control module to monitor EVAP system performance—such as detecting small or large leaks. The solenoid and associated wiring for this valve are located under the fuel tank, near the rear left side of the vehicle. It's a check valve-type unit with hoses connected and an electronic solenoid with its own harness. Possible failure points include: - The vacuum cut bypass solenoid or its electrical connections - Vacuum hoses (cracked, loose, or clogged) - The vacuum check valve itself Troubleshooting steps: 1. Test the vacuum cut bypass sensor for proper operation and physical damage. 2. Inspect all vacuum hoses for leaks or disconnections. 3. Check if the vacuum check valve is functioning correctly—replace it if necessary. 4. Conduct a full EVAP system inspection to ensure integrity. This issue can lead to failed emissions tests, so prompt diagnosis and repair are recommended.

Anonymous 2008-03-16 10:01

I have a 2005 Nissan Xterra with code P1491. Does anyone know what this means for my vehicle and where the component is located?

Anonymous 2008-03-16 10:17

mrquick1 wrote: 'Code P1491 on 2005 Nissan Xterra — does anyone know what it means and where it's located?' Please start a new thread for your specific issue. Include details such as engine size, mileage, recent maintenance, or modifications to help others assist accurately.