The Service Bay Tests are included on the scan tool for some systems depending upon vehicle make and model. The service bay tests initiate the operation of certain PCM controlled functions, assisting the technician in system diagnosis.
EVAP Service Bay Test
The EVAP service bay test is designed to enable the PCM to run the on-board EVAP system diagnostic. If the diagnostic detects any system leaks or component failures the PCM stores the appropriate DTC under Last Test Failed. Throughout the diagnostic test sequence the PCM uses the fuel tank pressure (FTP) sensor in order to monitor the vapor pressure in EVAP system. Unexpected changes in EVAP system pressure can indicate the incorrect operation of EVAP system components and detect system leaks.
The EVAP service bay test is an automated sequence of four individual EVAP test events. The following table provides an overview of each event:
Diagnostic Test Event | EVAP Purge Solenoid | EVAP Vent Solenoid | EVAP Vacuum Leak Pump | FTP Sensor Pressure, mm Hg (in H2O) |
|---|---|---|---|---|
First Event | OFF, CLOSED | OFF, OPEN | OFF for 10 Seconds, then ON for 30 seconds | Zero, then decreasing, negative pressure |
Second Event | OFF, CLOSED | ON, CLOSED | ON | Sudden pressure increase |
Third Event | OFF, CLOSED | ON, CLOSED | ON | Pressure decreases to lower limit and then stabilizes, vacuum decay test |
Fourth Event | ON, OPEN | ON, CLOSED | ON | Pressure returns to zero in less than 10 seconds |
The EVAP service bay test can require up to 15 minutes in order to run. If the test detects a fault in the first or second event, the test will end in less than 2 minutes. When the service bay test is complete, the EVAP I/M System Status updates to YES. In order to perform the EVAP service bay test with the scan tool follow the procedures below:
Important: Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. Fuel tank pressure may increase on a hot vehicle due to the thermal expansion of vapors in the fuel tank. Perform the EVAP service bay test when the temperature of the fuel is less than 35°C (95°F).
Important: Fuel tank fill levels can affect the results of the diagnostic procedure. The fuel level in the fuel tank should be between 25-75 percent of full.
- Install the scan tool.
- Turn ON the ignition, with the engine OFF.
- Ensure that the fuel filler cap is installed securely.
- Perform the scan tool Clear DTC function.
- Enable the EVAP Service Bay Test with the scan tool.
- If the scan tool displays Test in Progress, the service bay test is enabled.
- If the scan tool displays Test Failed, the test was not enabled. Exit the test screen on the scan tool and turn OFF the ignition for 30 seconds. After 30 seconds turn ON the ignition and enable the test again with the scan tool.
- DO NOT turn OFF the ignition or select EXIT on the scan tool during the Test in Progress display.
- WAIT until the scan tool displays Test Complete.
- Check for DTCs under Last Test Failed with the scan tool.
- No DTCs stored indicates that the EVAP system diagnostic has passed and no EVAP system faults are present.
- Any stored DTC indicates that an EVAP system fault exists. Go to the appropriate DTC table and perform the diagnostic procedure as necessary.
Check Mode
Check Mode can be used to increase the ability of the powertrain control module (PCM) to detect engine control system malfunctions. The PCM can be requested to operate in Check Mode by using the Output Controls feature of the scan tool. While in Check Mode operation the PCM will turn ON the malfunction indicator lamp (MIL) and record Freeze Frame data even on the first failure of a B type DTC. Not all engine control system diagnostics will be enhanced by Check Mode operation. The Check Mode service bay test can be performed while driving the vehicle in order to duplicate the customer concern. Those diagnostics most commonly known to benefit from Check Mode operation will be specified in the diagnostic procedure.
In order to activate the enhanced diagnostics of Check Mode operation, perform the following procedure:
Important: DO NOT turn OFF the ignition anytime during or after the operation of the vehicle in Check Mode. Observe and capture all Check Mode operation DTC and Freeze Frame information on the scan tool before turning OFF the ignition. Any DTC or Freeze Frame information that occurred during Check Mode operation will be cleared by the PCM when the ignition is turned OFF.
- Capture or save any DTC or Freeze Frame information on the scan tool before entering Check Mode operation. All DTC and Freeze Frame information will be cleared by the PCM when Check Mode is entered.
- Turn ON the ignition, with the engine OFF.
- Enter Check Mode operation with the scan tool from the Special Functions selection. Verify that the MIL is flashing which indicates that the Check mode request was received and accepted.
- Return to the Data List selection on the scan tool.
- DO NOT turn OFF the ignition after requesting Check Mode operation with a scan tool. The PCM will return to Normal Mode operation when the ignition is cycled from ON to OFF to ON.
- Start the engine.
- Operate the vehicle within the conditions under which the original concern was noted or within the Freeze Frame conditions that set the DTC.
- The Diagnostic Mode parameter in the scan tool data list can be viewed at anytime in order to verify that the vehicle is still operating in Check Mode.
- If the MIL illuminates while in Check Mode, observe and capture all DTC and Freeze Frame information with the scan tool.
- Check Mode operation can be terminated by cycling the ignition switch, or commanding Normal Mode with the scan tool.
