Infiniti Q45. Manual - part 483

DTC P1491 VACUUM CUT VALVE BYPASS VALVE

EC-571

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On Board Diagnosis Logic

NBS0023P

DTC Confirmation Procedure

NBS0023Q

CAUTION:

Always drive vehicle at a safe speed.

NOTE:
If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at
least 10 seconds before conducting the next test.
TESTING CONDITION:

●

Always perform test at a temperature of 5 to 30

°

C (41 to 86

°

F).

●

Before performing the following procedure, confirm that battery voltage is more than 11V at idle.

 WITH CONSULT-II

1.

Turn ignition switch ON.

2.

Start engine and warm it up to normal operating temperature.

3.

Turn ignition switch OFF and wait at least 10 seconds.

4.

Start engine and let it idle for at least 70 seconds.

5.

Select “VC CUT/V BP/V P1491” of “EVAPORATIVE SYSTEM” in “DTC WORK SUPPORT” mode with
CONSULT-II.

6.

Touch “START”.

DTC No.

Trouble diagnosis name

DTC detecting condition

Possible cause

P1491
1491

Vacuum cut valve bypass 
valve

Vacuum cut valve bypass valve dose not 
operate properly.

●

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 canister

●

EVAP purge port of fuel tank for clogging

●

Refueling EVAP vapor cut valve

●

Refueling control valve

SEF210Y

EC-572

DTC P1491 VACUUM CUT VALVE BYPASS VALVE

7.

When the following conditions are met, “TESTING” will be dis-
played on the CONSULT-II screen. Maintain the conditions con-
tinuously until “TESTING” changes to “COMPLETED”. (It will
take at least 30 seconds.)

If “TESTING” is not displayed after 5 minutes, retry from
step 3.

8.

Make sure that “OK” is displayed after touching “SELF-DIAG
RESULTS”. If “NG” is displayed, refer to 

EC-574, "Diagnostic

Procedure"

 .

Overall Function Check

NBS0023R

Use this procedure to check the overall function of vacuum cut valve bypass valve. During this check, the 1st
trip DTC might not be confirmed.

 WITH GST

1.

Remove vacuum cut valve and vacuum cut valve bypass valve as an assembly.

2.

Apply vacuum to port A  and check that there is no suction from
port B .

3.

Apply vacuum to port B  and check that there is suction from
port A .

4.

Blow air in port B  and check that there is a resistance to flow out
of port A .

5.

Supply battery voltage to the terminal.

6.

Blow air in port A  and check that air flows freely out of port B .

7.

Blow air in port B  and check that air flows freely out of port A .

8.

If NG, go to “

EC-574, "Diagnostic Procedure"

 .

ENG SPEED

More than 1,000 rpm

Selector lever

Suitable position

VHCL SPEED SE

More than 36 km/h (22 MPH)

B/FUEL SCHDL

1.0 - 10.0 msec

SEF211Y

SEF239Y

SEF530Q

DTC P1491 VACUUM CUT VALVE BYPASS VALVE

EC-573

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Wiring Diagram

NBS0023S

TBWM1244E

EC-574

DTC P1491 VACUUM CUT VALVE BYPASS VALVE

Specification data are reference values and are measured between each terminal and ground.

CAUTION:

Do not use ECM ground terminals when measuring input/output voltage. Doing so may result in dam-
age to the ECM's transistor. Use a ground other than ECM terminals, such as the ground.

Diagnostic Procedure

NBS0023T

1. 

INSPECTION START

Do you have CONSULT-II?

Yes or No

Yes

>> GO TO 2.

No

>> GO TO 3.

2. 

CHECK VACUUM CUT VALVE BYPASS VALVE OPERATION

 With CONSULT-II

1.

Turn ignition switch OFF.

2.

Remove vacuum cut valve and vacuum cut valve bypass valve as an assembly.

3.

Apply vacuum to port A and check that there is no suction from
port B.

4.

Apply vacuum to port B and check that there is suction from port
A.

5.

Blow air in port B and check that there is a resistance to flow out
of port A.

6.

Turn ignition switch ON.

7.

Select “VC/V BYPASS/V” in “ACTIVE TEST” mode with CON-
SULT-II and touch “ON”.

8.

Blow air in port A and check that air flows freely out of port B.

9.

Blow air in port B and check that air flows freely out of port A.

OK or NG

OK

>> GO TO 4.

NG

>> GO TO 7.

TER-

MINAL 

NO.

WIRE 

COLOR

ITEM

CONDITION

DATA (DC Voltage)

111

W/B

ECM relay
(Self shut-off)

[Engine is running]
[Ignition switch: OFF]

●

For a few seconds after turning ignition 
switch OFF

0 - 1.5V

[Ignition switch: OFF]

●

More than a few seconds after turning igni-
tion switch OFF

BATTERY VOLTAGE
(11 - 14V)

112

G/Y

Vacuum cut valve bypass 
valve

[Ignition switch: ON]

BATTERY VOLTAGE
(11 - 14V)

119

120

R
R

Power supply for ECM

[Ignition switch: ON]

BATTERY VOLTAGE
(11 - 14V)

PBIB3161E

PBIB3138E