Code Definition

P1491 — EVAP Vacuum Cut Bypass Valve

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Nissan

About P1491

P1491 is a manufacturer-specific powertrain diagnostic trouble code recorded for Nissan vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1491 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The EVAP vacuum cut bypass valve on Nissan vehicles bypasses the vacuum cut valve so the evaporative emission (EVAP) system can be drawn into vacuum and tested for leaks by the Engine Control Module (ECM). DTC P1491 indicates the ECM has detected the vacuum cut bypass valve is not functioning correctly during the leak test, for example it does not open or seal as needed so the expected vacuum is not achieved or held. This can be a mechanical valve fault, a vacuum hose problem, or a control issue. Symptoms are generally limited to the check engine light because the valve relates to the EVAP sel...

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