P1491 NISSAN Possible 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
First diagnose P1491 NISSAN code
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 terminals.
P1491 NISSAN Tech NotesIf 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
Cost of diagnosing the P1491 NISSAN code
Labor: 1.0The cost of diagnosing the P1491 NISSAN code is 1.0 hour of labor. The auto repair labor rates vary widely across the country, and even within the same city. Most auto repairs shops charge between $75 and $150 per hour.
When is the P1491 NISSAN code detected?Vacuum cut valve bypass valve does not operate properly.
P1491 NISSAN Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P1491 NISSAN MeaningThe 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 More InformationNeed more information on how to fix the P1491 NISSAN code?
Get Access to Factory Service Manuals