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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1446 (Engine Control System - 4.2L - Troubleshooting & Diagnosis) >> Diagnosis Information & Procedures >> Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure >> Diagnostic Aids

Diagnostic Aids

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Extreme high or low ambient temperatures may prevent the EVAP System Tests from initiating. Performing a visual inspection prior to running the EVAP Service Bay Test may prevent having to repeat the test. A loose fuel cap may cause a Service Bay Test to abort or fail and prevent the I/M System Status from updating. A failed or aborted test will require the vehicle to cool down in order to meet the enable criteria to run another test.

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the malfunction indicator lamp (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs).

The first failure of a type B DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met in order for the test to run again. These conditions may include a partial to complete engine cool down.

The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning ON, may cause the test to abort.

If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure

Step Action Yes No
1 Did you perform the Inspection/Maintenance (I/M) System Check? Go to Step 2  Go to Inspection/Maintenance (I/M) System Check 
2
  1. Select Special Functions with a scan tool.
  2. Determine if the vehicle is equipped with a Service Bay Test for the EVAP System.
Is the vehicle equipped with EVAP Service Bay Test?		 Go to Step 3  Go to Step 5 
3
  1. Ensure that the vehicle is within the Conditions for Running specified in the supporting text.
  2. Turn OFF all of the accessories, e.g., A/C, blower fan, etc.
  3. Following the directions on the scan tool, perform the EVAP Service Bay Test.
Did the EVAP System pass the Service Bay Test?		 Go to Step 8  Go to Step 4 
4
  1. Observe the scan tool Service Bay Test for an indication of why the test did not pass, e.g., failed DTC, test aborted, etc.
  2. Refer to the appropriate service information for diagnosis and repair of the condition as necessary.
Is the repair complete?		 - Go to Inspection/Maintenance (I/M) Complete System Set Procedure 
5
  1. Ensure that the vehicle is within the Conditions for Running specified in the supporting text.
  2. Turn OFF all of the accessories, e.g., A/C, blower fan, etc.
    3. IMPORTANT: Once the engine is started, DO NOT turn the engine OFF for the remainder of the procedure until the test is complete.
  3. Start the engine and idle.
    4. CAUTION: Refer to Road Test Caution in Cautions and Notices.
    IMPORTANT: In order for this test to run, the vehicle must operate in the following conditions:
  4. Acceleration at part throttle to 72 km/h (45 mph) with this speed maintained until the engine reaches operating temperature. This may be up to 8-10 minutes depending on the start up coolant temperature.
  5. Continue the operating conditions for an additional 3 minutes after the engine reaches operating temperature, or until the I/M System Status indicator updates to YES.
Did the EVAP System Status update to YES?		 Go to Step 8  Go to Step 6 
6 Observe the DTC Information, with a scan tool.
Does the scan tool indicate any failed DTCs?		 Go to Diagnostic Trouble Code (DTC) List Go to Step 7 
7
  1. Refer to Inspection/Maintenance (I/M) System DTC Table  to determine which DTCs are required to run in order to complete this test.
  2. Observe the Not Ran Since Code Cleared display, with a scan tool.
  3. Determine which of the DTCs required for a YES status has not run.
  4. Enter the DTC number in the Specific DTC menu of the scan tool.
  5. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC.
  6. Repeat the procedure until the scan tool indicates the diagnostic test has run.
  7. Repeat steps 4-6 for any additional required DTCs that have not run.
  8. Observe the I/M System Status display, with a scan tool.
Did the EVAP System Status update to YES?		 Go to Step 8  Go to Diagnostic Aids
8 Observe the Emission Related DTC portion of the I/M System Status display, with a scan tool.
Does the scan tool indicate any Emission Related DTCs set?		 Go to Diagnostic Trouble Code (DTC) List System OK
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