Engine-Codes - Nissan - P1491 Nissan

P1491 Nissan Code - Vacuum Cut Valve Bypass Valve

- Code Popularity: 110,828 Views
- Repair Importance Level: 3/3
- Repair Difficulty Level: 3/3
Table of contents

|What are the Possible Causes of the Code P1491 Nissan?

  • 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

|How to Fix the P1491 Nissan Code?

Start by checking 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's pins.

|Code P1491 Nissan 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

|What is the Cost to Diagnose the Code P1491 Nissan?

Labor: 1.0

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

Does your car have Safety Recalls? → Check here

|When is the P1491 Nissan Code Detected?

Vacuum cut valve bypass valve does not operate properly.

|What are Code P1491 Nissan 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.

Vacuum Cut Valve Bypass Valve

|Need more Information on the P1491 Nissan Code?

Need more information on how to fix the P1491 Nissan code? Get Access to Factory Service Manuals

|Need Help with the P1491 Nissan Code?

Get the P1491 Nissan code diagnosed by a professional: Find a repair shop in your area