2004 Scion xB 1.5L Small EVAP Leak P0456
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General Information: This vehicle came in with a check engine light with the code P0456. P0456 is a code for the EVAP system. The code states, “EVAP system very small leak detected”.
First Thoughts: I actually enjoy EVAP system problems. It is a great challenge for any mechanic. The codes can sometimes be miss leading. In some cases, an EVAP problem can be masked by codes from other systems like O2 sensor codes. (Fords are known for that problem)
Diagnostics: There are really only two go-to tools for me in any EVAP system diagnostics.
The first is my scan tool. It is a Snap-On Zeus. It allows me to command certain actuators on to either check the integrity of the part, the circuit, or to seal the whole EVAP system. Many advanced scan tools have this “bi-directional controls” feature.
The other tool is a smoke machine. This allows me to fill the EVAP system up with smoke. When smoke is present outside of the EVAP system, when it is supposed to be inside of it, I know there is a leak.
The first step I took to find the problem with this car was to start filling the EVAP system with smoke. The way I do that is by finding the green EVAP cap inside the engine compartment. Not all cars have this green cap, but most cars do. I remove the cap and connect the smoke machine.
I don’t start the smoke machine right away. I first have to connect my scan tool to make sure I can command the EVAP system to seal. I did this by using the bi-directional controls on the scan tool and commanding the EVAP vent valve shut.
I start the smoke machine and wait to see if there is any smoke. Most automotive smoke machines have a dial that you can watch to see if there is a leak. On my smoke machine, the dial goes all the way down when there is no leak, stays up when there is a leak, or varies in the middle depending on the severity of a leak.
The smoke machine indicated that there was a leak, and I could see smoke from the rear of the car.
A crucial component of the EVAP system is the gas cap. Many times, the o-ring of the gas cap will fail and cause a leak. But in this case, someone has already replaced the gas cap.
The only thing, though, is that they did not take off the old tether.
As you can see from the picture above, the tether is caught underneath the gas cap. This caused the new gas cap to not seal and leak.
After taking off the old tether and tightening the gas cap, no more leak!
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