Evaporative Emission System Diagnosis
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Evaporative Emission System Diagnosis
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Operating Instructions for the Evaporative Emission System Tester (EEST)
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Vehicle Setup
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1.
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Note
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A large difference between the vehicle temperature and shop temperature will seriously affect the accuracy of the tests. Always allow enough time, at least 15 minutes, for the vehicle temperature to adjust to the shop temperature. Refer to Temperature Variation Instructions for more information about vehicle versus shop temperatures.
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Engine OFF, open the hood. Position a large fan to blow air under the vehicle onto the fuel tank area.
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2.
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Connect the red battery clip from the tester to the positive battery terminal.
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3.
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Note
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The vehicle battery must be fully charged for optimum tester performance.
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Connect the black battery clip from the tester to chassis ground.
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Flowmeter Test - Leak Detection
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1.
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Open the Nitrogen tank valve and turn the NITROGEN/SMOKE valve on the front control panel to NITROGEN.
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2.
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Connect the hose to the correct test orifice on the bottom front of the tester. For orifice size, refer to the GM Service manual for the vehicle being tested. The vehicle specific information can be found in service procedures for DTCs that relate to evaporative emission (EVAP) system leaks.
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3.
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Press and release the remote switch to activate the tester.
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4.
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Position the sliding red flag on the flowmeter to align with the floating indicator. When the red flag is set, press and release the remote switch to deactivate the tester.
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5.
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Remove the hose from the test orifice and install the hose onto the vehicle. For proper connection location, and the special tool numbers for any adapters that may be required, refer to the service procedures for DTCs that relate to EVAP system leaks.
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6.
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Seal the EVAP system per instructions in the service procedures for DTCs that relate to EVAP system leaks. Most systems can be sealed using a scan tool output control for the EVAP canister vent solenoid valve, other systems require that the vent system be plugged.
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7.
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Note
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Larger volume fuel tanks, and/or those with lower fuel levels, may require several minutes to fill with nitrogen.
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Static buildup may cause the float indicator to stick. It may be necessary to tap on the flowmeter to free up the float.
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Press and release the remote switch to activate the nitrogen flow and fill the system.
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8.
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Compare the stable floating indicator position to the red flag.
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ABOVE the red flag, the result is UNACCEPTABLE, FAIL-Go to Smoke Procedure
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BELOW the red flag, the result is ACCEPTABLE, PASS-Test complete
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9.
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Press and release the remote switch to deactivate the tester.
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Smoke Procedure - Locate the Leak
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1.
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Note
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It is not recommended to use the tester in an outside repair bay area because wind and sunlight may affect temperature and your ability to see the smoke.
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Turn OFF any fans that may cause air movement around or near the vehicle.
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2.
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Note
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Completely unwind the nitrogen/smoke hose from the bracket to optimize the tester's performance.
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Connect the nitrogen/smoke hose to the vehicle as directed in the service procedures. Some vehicles require that the nitrogen/smoke hose be connected at the front of the EVAP system at the EVAP service port. An adapter may be necessary. Other vehicles require the connection be made at the rear of the system using an adapter at the fuel fill cap. Consult the service procedures for DTCs that relate to evaporative emission (EVAP) system leaks for vehicle specific instructions regarding connection location and adapters.
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3.
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Open the nitrogen tank valve and turn the NITROGEN/SMOKE valve on the control panel to SMOKE.
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4.
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Note
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The remote switch operates in a push ON, push OFF fashion.
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Press and release the remote switch to activate the tester and inject smoke into the EVAP system.
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5.
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Verify smoke has filled the EVAP system by opening the system opposite the end where smoke is injected. When injecting smoke at the service port, remove the fuel fill cap, or temporarily leave the EVAP canister vent valve open, until smoke is observed. Then close the system and continue testing. If using a special tool fuel fill cap adapter at the filler neck, vent the system at the service port until smoke is observed then close the system to continue with the test.
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6.
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Note
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Inject smoke in less than 2-minute cycles for optimum tester performance.
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Press and release the remote switch to deactivate the tester.
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7.
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Note
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For optimum visual smoke performance, deactivate the smoke flow and allow the system pressure to drop. Allowing the smoke to exit small holes at a low flow rate greatly enhances visibility.
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Introduce smoke into the system for an additional 60 seconds. Continue to spray in smoke at 15 second intervals as necessary.
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8.
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Using the a high-intensity white light , inspect the entire EVAP system path, and look for the source of the leak indicated by the exiting smoke. Introduce smoke at 15 s intervals, as needed, until leak source is identified.
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Temperature Variation Instructions
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The Concern
Ideal circumstances for conducting the EVAP Flowmeter Test require equal temperatures between the nitrogen gas and the vehicle EVAP system. Significant differences in temperature between them can result in a flow or pressure change during testing, causing misleading results. Typically, the Evaporative Emissions System Tester is stored indoors, approximately 21°C (70°F). Vehicles brought in for diagnosis may have an EVAP system at significantly different temperatures -40 to +43°C (-40 to +110°F).
For Example
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Note
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With no temperature difference between the nitrogen gas and EVAP system, the resulting vehicle EVAP system pressure will remain stable at 13 inches H2O once pressurized, providing no leaks are present.
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When the EVAP Flowmeter Tests are performed with significant differences in temperature between the nitrogen gas and the vehicle EVAP system, the following results can occur:
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An increase in flow during the flowmeter test can be caused by a vehicle"s warm EVAP system cooling down.
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A decrease in flow during the flowmeter test can be caused by a vehicle"s cool EVAP system warming up.
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The Solution
When working on a vehicle with significant temperature differences between the vehicle EVAP system and the nitrogen gas, allow the vehicle EVAP system temperature to stabilize as close as possible to the temperature of the nitrogen gas before conducting the Flowmeter Test.
