On Board Diagnosis Logic

NOTE: If DTC P1456 is displayed with P1442, perform TROUBLE DIAGNOSIS FOR DTC P1456 first.

This diagnosis detects very small leaks in the EVAP line between fuel tank and EVAP canister purge volume control solenoid valve, using vapor pressure in the fuel tank in the same way as conventional EVAP small leak diagnosis.

If ECM judges a leak which corresponds to a very small leak, the very small leak P0456 will be detected.

If ECM judges a leak equivalent to a small leak, EVAP small leak P1442 will be detected.

If ECM judges there are no leaks, the diagnosis will be OK.

Fig 1: EVAP Control System Diagram

Courtesy of NISSAN MOTOR CO., U.S.A.

DTC DETECTING CONDITION CHART

DTC No.	Trouble diagnosis name	DTC detecting condition	Possible cause
P0456 0456	Evaporative emission control system very small leak (negative pressure check)	EVAP system has a very small leak. EVAP system does not operate properly.	Incorrect fuel tank vacuum relief valve Incorrect fuel filler cap used Fuel filler cap remains open or fails to close. Foreign matter caught in fuel filler cap. Leak is in line between intake manifold and EVAP canister purge volume control solenoid valve. Foreign matter caught in EVAP canister vent control valve. EVAP canister or fuel tank leaks EVAP purge line (pipe and rubber tube) leaks EVAP purge line rubber tube bent Blocked or bent rubber tube to EVAP control system pressure sensor Loose or disconnected rubber tube EVAP canister vent control valve and the circuit EVAP canister purge volume control solenoid valve and the circuit Absolute pressure sensor Fuel tank temperature sensor O-ring of EVAP canister vent control valve is missing or damaged Water separator EVAP canister is saturated with water EVAP control system pressure sensor Refueling control valve ORVR system leaks Fuel level sensor and the circuit Foreign matter caught in EVAP canister purge volume control solenoid valve

CAUTION:

Use only a genuine NISSAN fuel filler cap as a replacement. If an incorrect fuel filler cap is used, the MIL may come on.
If the fuel filler cap is not tightened properly, the MIL may come on.
Use only a genuine NISSAN rubber tube as a replacement.