![]() ![]() If that does not work, you may want to try the new Bullseye leak detection system from Automotive Test Solutions. When diagnosing EVAP system problems we usually just need a smoke machine that is connected to CO 2 or nitrogen (not air pressure) to move the smoke through the EVAP system. Since loose and defective gas caps are only to blame for a part of EVAP issues, when vehicles return with EVAP codes, it is necessary to properly diagnose them. This is why some techs delete the EVAP code and tell the vehicle owner to come back for a diagnosis if the MIL comes back on. 1 cause of a motorist’s illuminated check engine light is a gas cap that they did not tighten after refueling. In this article, I will provide you with some of the principles that you need to know to be successful at diagnosing and repairing EVAP system problems, especially finding those pesky little leaks. It becomes our problem when the system does not hold a vacuum or pressure and illuminates the Malfunction Indicator Lamp (MIL). If the system does not leak more than the specified amount (0.010, 0.020 or 0.040 inch), the system receives a pass. The PCM has a specific amount of time programed into the test procedure that checks the system for hold vacuum or pressure, depending on the system. When the EVAP system needs to test itself for leaks, the PCM pulses the purge valve open just long enough to create a vacuum before it closes the vent valve along with itself. The vent valve is normally OPEN, which means without a command from the PCM, the valve is OPEN, allowing the system to flow vapors. This means with no command from the Powertrain Control Module (PCM), the valve prevents the vacuum from purging EVAP vapors from the canister. ![]() Remember the following: the purge valve is normally CLOSED. If you break the system down into small sections, it’s easier to diagnose. Since EVAP Diagnostic Trouble Codes (DTCs) are among the top codes that we have to diagnose, we need a good understanding of the system. ![]()
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