Source:
The information and products that work alongside your scan tool for a complete repair.
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Issue one: P0442 fault code – Small leak detected in evaporative system
The easiest check to perform first with any evaporative system (evap) leak is to make sure the fuel cap is present and tightened properly. Even if the cap is tight, it may be the cause of the leak, but in this case, someone has already tightened the cap.
After that easy check, you should look at the freeze frame data with your scan tool. This data contains a listing of what was occurring at the time the code was set. Depending on the vehicle, some of the data available may include how long the engine was running, the engine and vehicle speed, engine temperature, and possibly the fuel level. All of this information may assist you in determining what caused the fault. Having it available to you will also enable you to operate the vehicle under the same conditions after the repair to make sure the code doesn’t reset.
After you have the freeze frame data, refer to your vehicle information source to determine what the enabling criteria (the operating conditions) are to trigger the fault code. This is critical if you’ll be performing a drive cycle to verify your repair.
Most vehicles use similar criteria for monitoring the evap system and will need 15 to 85 percent fuel level. If the fuel level is either above 85 percent or below 15 percent, the test won’t run, and you’ll likely spend hours and multiple drive cycles attempting to validate your repairs without success. These vehicles also monitor engine and ambient air temperature. Upon startup, the two temperatures need to be within 10 degrees of each other. If not, the computer assumes it’s not a cold start and will not perform an evap test.
Another common condition that’s difficult to overcome is the ambient air temperature. Many vehicles will not run an evap test if the air temperature is above 104 degrees F or below 32 degrees F. That’s because tank pressure can change drastically either above or below those temperatures, making leak detection difficult.
The evap monitor test needs multiple tests to either pass or fail, so your scan tool can be used to look at
Mode $06 information to see which part of the evap system malfunctioned. This is done by observing the Mode $06 data to see specifically which part of the evap test failed, which allows you to get information from your vehicle information system about that aspect of the evap test process. You can then use that as a starting point for your testing.
Your scan tool also has the ability to control some features of the evap monitor test as well as monitor the datastream to see if it’s functioning. Many scan tools will allow you to perform what is commonly known as a “Service Bay Test”, basically an electrical test of the purge and vent functions of the system. Using bidirectional controls and monitoring various PID’s, you will also be able to see if the purge valve is opening and closing properly by monitoring oxygen sensor voltage, or, with some vehicles, fuel tank pressure.
One of the best tools to locate evap system leaks is a diagnostic smoke machine. Connecting a smoke machine allows you to easily observe any trace of smoke that would indicate a leak, but in some cases, you will need to use the smoke machine and a little ingenuity to find a leak. I have had multiple vehicles that had a faulty purge solenoid which did not completely close, thereby allowing the system to lose pressure (vacuum).
Even though the system was still closed to the atmosphere, the computer system detected a leak. The way I tested for a faulty solenoid was to connect the smoke machine to the system, then disconnect the hose from the purge solenoid to determine if there was a leak. A helpful hint for finding traces of smoke, especially in a brightly lit shop, is to wave a laser pointer around the area of a suspected leak. The laser light will highlight any faint traces of smoke.