Purge Vent Solenoid P0455
How do you test the EVAP system using a bidirectional Scan Tool?
First of all, you can not check the system if you have no idea how the PCM tests the circuit. If you have a basic knowledge of the system, this will go a long way when you test EVAP System.
There are a number of ways to test the EVAP circuit with or without a scan tool.
A good scan tool should be able to perform bi-directional control functions, for example, you can turn a solenoid on and off and confirm its operation.
Here is a good example, let's say a vehicle comes into your shop with a code P0455 gross leak. You probably will start to look at the gas, so let's say the gas cap was already replaced, now what would you do?
Remember on a previous page "Basic EVAP Overview." I had mention the vent valve only closes during testing. During testing the vent valve closes so the system can pull a vacuum.
But if the vent valve is stuck open when the purge valve is a command on a stuck open vent valve will not be able to pull a vacuum.
So when the monitor runs a test on the circuit, it will fail, and if it fails twice the MIL will come with a DTC.
So that is pretty obvious a stuck open or missing component will cause a P0455 code with a MIL on the dashboard.
But did you know a stuck close purge valve will also cause the same problem, this was a surprise to me? A stuck closed purge solenoid will also prevent the vacuum from building in the EVAP system, and the result will be a gross leak and DTC P0455.
So a large leak will prevent a vacuum from building up, so it's a good idea to confirm the Purge / Vent Solenoid are functional.
This can be accomplished with a vacuum pump, smoke machine, amp meter or a bi-directional scan tool.