Engine-Codes - Nissan - P1491 Nissan

P1491 Nissan Code - Vacuum Cut Valve Bypass Valve

- Code Popularity: 118,207 Views
- Repair Importance Level: 3/3
- Repair Difficulty Level: 3/3
Table of contents
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What are the Possible Causes of the DTC P1491 Nissan?

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
  • Vacuum cut valve bypass valve
  • Vacuum cut valve
  • Bypass hoses for clogging
  • EVAP control system pressure sensor and circuit
  • EVAP canister vent control valve
  • Hose between fuel tank and vacuum cut valve clogged
  • Hose between vacuum cut valve and EVAP canister clogged
  • EVAP purge port of fuel tank for clogging

Code Tech Notes

If the EVAP canister is OK, and there are no other visual damage to the EVAP system (e.g. loose or broken hoses), replacing the vacuum cut valve bypass valve takes care of the problem.

There is a factory service bulletin for all 1998-2002 Nissan models.
1998-2002 Nissan Factory Service Bulletin OBDII Code P1491

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How to Fix the DTC P1491 Nissan?

Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

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What is the Cost to Diagnose the Code?

Labor: 1.0

The cost to diagnose the P1491 Nissan code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.

When is the Code Detected?

Vacuum cut valve bypass valve does not operate properly.

What are Code Possible Symptoms?

  • Engine Light ON (or Service Engine Soon Warning Light)

What Does the P1491 Nissan Code Mean?

The vacuum cut valve and vacuum cut valve bypass valve are installed in parallel on the EVAP purge line between the fuel tank and the EVAP canister.
The vacuum cut valve prevents the intake manifold vacuum from being applied to the fuel tank. The vacuum cut valve bypass valve is a solenoid type valve and generally remains closed. It opens only for on board diagnosis.
The vacuum cut valve bypass valve responds to signals from the ECM. When the ECM sends an ON (ground) signal, the valve is opened. The vacuum cut valve is then bypassed to apply intake manifold vacuum to the fuel tank.

P1491 Nissan Code - Vacuum Cut Valve Bypass Valve

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