EVAP Running Loss System Test
To start the testing, conditions of stable purging and vehicle speed must be satisfied. During the first stage, the EVAP canister vent solenoid is closed while the EVAP canister purge valve remains open, applying and building vacuum in the system as indicated by the fuel tank pressure (FTP) sensor. This phase checks for major leaks in the EVAP system.
In the second stage, the EVAP canister purge valve closes and the system looks for minimal decay rate in the EVAP vacuum, indicating the absence of any small EVAP system leaks.
The last stage is entered only if stage two of the leak test has failed and checks whether the failed test was due to excess vapor generation. It monitors fuel vapor generation rate. Initially the canister vent solenoid is opened to equalize EVAP system pressure to atmosphere. Then the canister vent solenoid is closed allowing pressure to build, if vapor generation is present in sufficient quantity. If the rate of generation is found to be too high, the EVAP running loss system leak test is aborted. If not, then a small leak is diagnosed.
Scheme 62
- Verify the customer concern is with the evaporative emission (EVAP) system.
- Visually inspect for the following obvious signs of mechanical damage.
- If the concern remains after the inspection, connect the scan tool to the data link connector (DLC) located beneath the instrument panel and select the vehicle to be tested from the scan tool menu. If the scan tool does not communicate with the vehicle: Check that the program card is correctly installed. Check the connections to the vehicle. Check the ignition switch position.
- If the scan tool still does not communicate with the vehicle, refer to the scan tool manual.
- Carry out the DATA LINK DIAGNOSTICS test. If the scan tool responds with: CKT914, CKT915 or CKT70 = ALL ECUS NO RESP/NOT EQUIP, refer to «MODULE COMMUNICATIONS NETWORK»(ref-210196) . NO RESP/NOT EQUIP for PCM, refer to the appropriate INTRODUCTION article. SYSTEM PASSED, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and carry out the PCM KOEO self-test.
- If the DTCs retrieved are related to the concern, refer to the appropriate INTRODUCTION article.
- If the concern remains after the inspection, determine the symptom, and refer to the appropriate INTRODUCTION article.
Scheme 63
| CAUTION | The canister vent solenoid must not be energized for more than nine minutes at one time. Once the canister vent solenoid is energized and de-energized, adequate time must be allowed for the component to cool adequately. Failure to allow the component to cool may create a false failure in the diagnostics, causing unnecessary repairs. |
- Connect the scan tool and select the output test mode.
- If PID monitors are not active, select PIDs.
- Select the fuel tank pressure (FTP) and the volts (V) parameter identification (PID) for monitoring.
- Select the ALL OFF mode.
- Close the canister vent solenoid by pushing the START button on the scan tool.
