Evaporative Emissions Control Systems (EVAP)

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

2. 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

3. 2 Types of Systems • Non-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.

4. Components: • Carbon canister • 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

5. 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

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

7. Function: • Purging is closely controlled • 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

8. Finding Faults • Two types of complaints: • 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

9. 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

10. 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

11. 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

12. 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

13. Toyota Evaporative Emissions