Code Definition

P1491 — EVAP Vacuum Cut Bypass Valve

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

About P1491

P1491 is a manufacturer-specific powertrain diagnostic trouble code recorded for Infiniti 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

DTC P1491 relates to the EVAP vacuum cut valve and its bypass system on these Nissan and Infiniti vehicles, and is set when the Engine Control Module (ECM) finds the unit is not functioning correctly as a whole. The vacuum cut valve sits in the EVAP line between the fuel tank and the charcoal canister and normally prevents intake manifold vacuum from reaching the fuel tank, while the bypass valve opens during onboard diagnosis to apply that vacuum for the leak test. Where the companion circuit code targets the bypass valve wiring, P1491 points to the main vacuum cut valve or the overall vacuum...

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