Evaporative Emissions Control Systems (EVAP) Purpose Enhanced and Non-Enhanced Components Function Finding Faults

Purpose: To trap and hold gasoline vapors (HC) To deliver vapors to engine airflow for complete burning Provides system ventilation to allow purging Provides pressure relief to prevent excess pressure inside fuel tank

2 Types of Systems Non-Enhanced Enhanced Diagnostic ability is limited to purge detection and monitoring Enhanced Monitors purge flow Monitors system integrity Leak checking 1996-2000: leak checking to .040 in. 2000-up: leak checking to .020 in.

Components: Carbon canister Purge valve/ Purge solenoid Vacuum lines Traps and holds fuel vapors for burning by engine Purge valve/ Purge solenoid Controlled by PCM to allow canister purging during certain conditions Vacuum lines Connect tank to canister Connect canister to engine Fuel tank filler cap Seals fuel tank Allows for pressure relief Prevents excessive vacuum from collapsing tank Fuel expansion tank Prevents liquid fuel from entering canister Fuel Tank Pressure Sensor (Enhanced) Vent valve (Enhanced) Provides fresh air for system purging Can be used to seal system to check for leaks

Function: As fuel heats up: vapors form and are vented to canister Canister is filled with activated charcoal Fuel vapors attach to carbon surface 1 gram of charcoal contains surface area equal to ¼ acre Holds 1/3 of its own weight in fuel vapors As system is purged, vapor molecules are pulled from carbon surface

Function: Pressure build-up is caused by: Volatility rates Fuel tank size Fuel level inside tank Fuel slosh Temperature Fuel return

Function: Purging is closely controlled Purging is allowed: Excess fuel vapors can upset air/fuel ratio Purging is allowed: Closed loop Cruising speeds Purging is not allowed: Open loop Idle or deceleration WOT

Finding Faults Two types of complaints: Retrieve DTC’s Fuel vapor smell MIL illumination Retrieve DTC’s Check freeze frame data for ECT and VSS Check TSB‘s, recalls and PCM reflashes DTC’s: Purge control circuit failures Purge flow failures Leak detection DTC’s

Finding Faults Follow manufacturer’s diagnostic troubleshooting procedure Purge control circuit failures: can be checked with bidirectional scan tool Command purge valve on and listen for clicking sound With valve commanded on check for air flow through valve Check power and ground wires with voltmeter Purge valve can be manually activated with jumper wires

Finding Faults Purge flow failures: can be caused by leakage or restriction preventing purge Smoke machine: insert probe into test port and watch machine’s flow meter Proper flow eliminates possibility of restriction in system Improper flow indicates system is restricted: isolate system and continue checking

Finding Faults Leak checks: connect smoke machine and close vent solenoid Vent solenoid can be closed with scan tool, manually cycled with jumper wires or vent pinched with suitable tool Smoke machine should indicate no flow if system is free from leaks If leaks are present, smoke will be visible

Locating Leaks Smoke testing: uses low pressure smoke introduced to system from test port Allows for visual leak detection Nitrogen gas pressurization Very low pressure (> 1 psi) Uses sound amplification for detecting leaks

Toyota Evaporative Emissions