DTC P0442, P0456: EVAPORATIVE EMISSION CONTROL SYSTEM LEAK DETECTED (SMALL LEAK/VERY SMALL LEAK) CIRCUIT DESCRIPTION The vapor pressure sensor and the VSV for CCV (Canister Closed Valve) are used to detect abnormalities in the EVAP (Evaporative Emission) control system. The ECM determines whether there is an abnormality in the EVAP control system based on the vapor pressure sensor signal. DTC P0442 or P0456 is set by the ECM when evaporative emissions leak from the components within the dotted line in Fig. 277 below, and when the vapor pressure sensor malfunctions. Fig. 277: Identifying Evaporative Emission Control System Circuit Description Courtesy of TOYOTA MOTOR SALES, U.S.A., INC. Fig. 278: DTC Chart Courtesy of TOYOTA MOTOR SALES, U.S.A., INC. Fig. 279: Evaporative Emission Control System Graph (Leak Check) Courtesy of TOYOTA MOTOR SALES, U.S.A., INC. MONITOR DESCRIPTION The ECM checks the EVAP (Evaporative Emission) system using the vapor pressure sensor, CCV (Canister Closed valve), and VSV (Vacuum Switching Valve) for EVAP. The ECM closes the EVAP system and introduces negative pressure (a vacuum) into it. The ECM then monitors the internal pressure using the vapor pressure sensor. (Refer to Fig. 277 ) The ECM checks for leaks in the EVAP system by introducing a highly negative pressure from the intake manifold, by signaling the VSV for EVAP to open with the VSV for CCV (vent) closed. After sufficient time has elapsed, the fuel tank develops a highly negative pressure and the VSV for EVAP is then closed. The ECM monitors the pressure rise (vacuum loss) in the fuel tank. If the pressure rapidly rises, the ECM determines that there is a leakage from the EVAP system, and illuminates the MIL and sets a DTC. If the leakage is large, DTC P0442 is set. If it is small, DTC P0456 is set. I would try a new cap first...PCV has nothing to do with this code!
Friday, February 27th, 2009 AT 3:35 PM