# Error Code P1491



## polynet (Jul 11, 2006)

Anybody have issues with code P1491? I thought it was a Gas Cap issue cause the NJ gas guys NEVER close my cap correctly. I got tired of looking at the light and went to AutoZone and got the readout.

Error P1491: Vacuum Cut Valve Bypass Valve

Anybody know what it means or how critical it is?

Thanks,
Paul


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## smj999smj (Jan 1, 2006)

Classification:
EC02-008

Reference:
NTB02-033

Date:
March 21, 2002

DTC 1491 (VACUUM CUT VALVE BYPASS VALVE) DIAGNOSIS

APPLIED VEHICLE(S):
1998-2002 All Models

SERVICE INFORMATION

This bulletin is an aid to the diagnostic procedures in the Service Manual for DTC P1491.

If one of the applied vehicles has the MIL "ON" with DTC P1491 (Vacuum Cut Valve Bypass Valve) stored in Self-Diagnostic Results, use the service procedure in this bulletin and the appropriate Service Manual to help you diagnosis the incident, if it should occur.

SERVICE PROCEDURE







1. Confirm the Vacuum Cut Valve is installed correctly (See Figure 1).

NOTE :

^ The Vacuum Cut Valve will not work correctly and a DTC will be stored if it is installed upside-down.

^ The Vacuum Cut Valve is a white plastic valve near the fuel tank and EVAP canister.


2. Connect CONSULT-II and turn the ignition key to "N" (do not start the engine).

3. On CONSULT II, select ENGINE - DATA MONITOR - SELECTION FROM MENU - EVAP SYSTEM PRESSURE SENSOR.

4. Note the EVAP System Pressure Sensor Voltage Confirm that it is reading in a normal range for a key ON arid engine OFF condition.

NOTE :For 2001 models and earlier:

^ Voltage in step 4 should be near 3.36 volts.

^ The normal range is between 3.32 - 3.40 volts.


For 2002 models:

^ Some 2002 models use a new type EVAP System Pressure Sensor with different operational characteristics.

^ Refer to the EC section of the appropriate Service Manual to determine which type sensor your vehicle is equipped with.

^ Models that use the new type EVAP System Pressure Sensor will have a voltage reading that varies with changes in the "barometric" pressure (atmospheric air pressure that changes with altitude and/or weather conditions).

^ The usual voltage range obtained in step 4 with the new type EVAP System Pressure Sensor is between 3.8 and 4.2 volts. Because this range will vary with barometric pressure, it is best to compare readings with a known good vehicle.

^ Some 2002 models use the earlier type EVAP System Pressure Sensor (same as used on 2001 and earlier models). The normal range for the earlier type is 3.32 to 3.40 volts and does not vary with barometric pressure.


5. Start the engine. Observe the EVAP System Pressure Sensor voltage.

^ If the value has reduced 0.04 volts or more from the reading obtained in step 4, the EVAP Canister Purge Volume Control Solenoid Valve may be leaking.

^ Refer to the EC section of the appropriate Service Manual for inspection procedures of the EVAP Canister Purge Volume Control Solenoid Valve, DTC P1444.


NOTE :The EVAP Canister Purge Volume Control Solenoid Valve is located in the engine compartment.

6. Perform the DTC Confirmation Procedure for DTC P1491. Refer to the EC section of the appropriate Service Manual for confirmation procedure steps and driving conditions.

7. If the DTC confirmation results are NG, do the following:

a. Refer to the EC section of the appropriate Service Manual to determine if the vehicle is equipped with On-Board Refueling Vapor Recovery (ORVR).

^ If the vehicle has ORVR, go to b.

^ If the vehicle does NOT have ORVR, go to step 8.










b. Place a clamp on the Refueling EVAP Vapor Line near the fuel tank. The Refueling EVAP Vapor Line is the larger hose (see figure 2). Use hose clamp (3M P/N # 08556-1), found in Fuel Injector Cleaning Kit J-45701, or equivalent.

c. Retry DTC Confirmation Procedure

d. If the result is now OK, the Refueling Control Valve may be leaking and should be inspected. Refer to the EC section of the appropriate Service Manual for Refueling Control Valve inspection procedures.

8. If the DTC confirmation is still NG after step 7, or the vehicle is not equipped with ORVR, do the following:

a. Disconnect two (2) lines from the Vacuum Cut Valve. One that goes to the fuel tank and one that goes to the EVAP Canister (see figure 1).

b. Use a hand vacuum pump to check each of the two (2) disconnected hoses for free flow. Make sure they are clear into the fuel tank (vent line) and into the EVAP Canister (see figure 2).


NOTE :

^ Figure 2 includes ORVR system. Refer to the appropriate service manual to determine if your vehicle has ORVR or not.

^ The lines between the Vacuum Cut Valve and Fuel Tank, and between the Vacuum Cut Valve and EVAP Canister may go through a metal line. Make sure the lines are clear between the Vacuum Cut Valve and Fuel Tank, and between the Vacuum Cut Valve and EVAP Canister, including any metal lines.

c. If any blockage is found, determine the cause and repair as necessary. Blockage in either of these lines will cause a DTC.


9. If all of the above checks do not locate the source of the incident, refer to the appropriate Service Manual for further DTC P1491 diagnosis.


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## golfer (Aug 21, 2006)

further to :

[URL=http://imageshack.us][/URL]

[URL=http://imageshack.us][/URL]


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## fusecon (Feb 25, 2005)

*P1491 P1444 PO325*



polynet said:


> Anybody have issues with code P1491? I thought it was a Gas Cap issue cause the NJ gas guys NEVER close my cap correctly. I got tired of looking at the light and went to AutoZone and got the readout.
> Error P1491: Vacuum Cut Valve Bypass Valve


We had our check engine light go on about a month back: P1491, P1444, and knock sensor. Place we took it to couldn't find anything wrong, then reset it. Next day, only one code popped up: P1444. So, the P1444 must have set off the other two. We had to get the EVAP Canister Purge Solinoid replaced. A very expensive part ($150 if you can get it online). But replacement is easy. We had the shop do this and paid a little more. Eventually I'll get one of those OBD II scanners to do some troubleshooting before taking it to be fixed.

Anyway, good luck. Hope it wasn't your charcoal canister with charcoal in the evap lines.

-dan


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## Markieo (Oct 31, 2016)

I just had a code PO 505, AND A PO 1491 . WHAT IS THE PROBLEM , these Nissan are full of problems, every time it brings up different codes, this is the first and last time I will ever own a Nissan, is a Disaster from the very beginning, spent over $1000 , in repair and now got 2 new codes listed above.


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