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

4. 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

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 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

8. 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

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