P0456

DTC P0456 EVAPORATIVE EMISSION CONTROL SYSTEM LEAK DETECTED (VERY SMALL LEAK)

CIRCUIT DESCRIPTION

DTC Detecting Condition:

The vapor pressure sensor and the canister closed valve (CCV) are used to detect abnormalities in the evaporative emission control system. The ECM decides whether there is an abnormality in the evaporative emission control system based on the vapor pressure sensor signal. DTC P0442 or P0456 is recorded by the ECM when evaporative emissions leak from the components within the dotted line in Fig 1. , or when the vapor pressure sensor malfunctions.

HINT: Typical DTC output of each trouble part.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions Part 1:

Typical Enabling Conditions Part 2:

Typical Malfunction Thresholds:

Monitor Result (mode 06 Data):

The evaporative emission system consists of the vapor pressure sensor, the CCV (Canister Close Valve), the pressure switching valve and the EVAP VSV (Purge VSV), those are used to detect malfunction in the system by ECM.
This test will run once per driving cycle provided the ECM when detects stable vapor pressure in the fuel tank. While the vehicle is being driven on rough or winding roads, the movement of the fuel in the tank will cause unstable fuel tank vapor pressure and the diagnostic test will not executed.
The ECM performs the following steps:
a. The CCV is closed. (shutting the system)
b. The fuel tank pressure stability is checked. The diagnostic is disabled if the pressure change is more than specified value.
c. The EVAP VSV is opened. This introduces a negative pressure from the intake manifold to the fuel tank.
d. The EVAP VSV is closed and the negative pressure is sealed in the fuel tank.
e. The ECM monitors the increase in fuel tank pressure for;
1. Rapid increase in the internal pressure, i. e. a large leak: 0.040" or more
2. A pressure rise just above normal, i. e. a small leak: 0.020".

If the ECM detects either of above conditions, it will interpret this as a leak in the EVAP system. The ECM will illuminate the MIL (2 trip detection logic) and set a DTC.

INSPECTION PROCEDURE