P0456

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

CIRCUIT DESCRIPTION

DTC Detection Condition:

The vapor pressure sensor and the VSV for 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, P0455 or P0456 is recorded by the ECM when evaporative emissions leak from the components within the dotted line in figure 1, or when the vapor pressure sensor malfunctions.

HINT: Typical DTC output of each trouble part.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Monitor Result (Mode 06 Data):

The evaporative emission system consists of the vapor pressure sensor, the canister close valve (CCV), the VSV for purge flow switching valve and the EVAP VSV (Purge VSV). These are used to detect malfunction in the system by ECM.

This test will run once per driving cycle when the ECM 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 be executed. The ECM performs the following steps:
a. Closes the canister close valve (CCV) (shuts the system).
b. Checks the stability of the fuel tank pressure. If the variation in the pressure is greater than the specified value, disables the diagnosis.
c. Opens the EVAP VSV to introduce negative pressure (vacuum) from the intake manifold into the fuel tank.
d. Closes the EVAP VSV to seal the fuel tank for storing the negative pressure.
e. Monitors the negative pressure in the fuel tank for:
1. Rapid decrease, i.e. a large leak, 0.040 inch or more
2. Decrease greater than the normal value If the ECM detects either of above conditions, the ECM interprets this as a leak in the EVAP system. The ECM will illuminate the MIL (2 trip detection logic) and set a DTC.

INSPECTION PROCEDURE

HINT:
- When using the hand-held tester, follow the procedures under the title "Hand-held tester" .
- When using the OBD II scan tool, follow the procedures under the title "OBD II scan tool (excluding hand-held tester)" (see the procedures after the "Hand-held tester" procedures).
- Always troubleshoot DTCs P0441 (purge flow), P0446 (CCV), P0451, P0452 and P0453 (evaporative pressure sensor) before troubleshooting DTCs P0442 or P0456.
- Ask the customer the following questions:
1. When the MIL came on, if the fuel tank cap was loose and if it was then tightened.
2. When refueling, if the fuel tank cap was loose.
If the fuel tank cap was loose, that is why the DTC was stored.
If the fuel cap was not loose or if the customer cannot remember, troubleshoot according to the procedures.

- Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine condition when malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.
- If the ENGINE RUN TIME in the freeze frame data is less than 200 seconds, carefully check the vapor pressure sensor.