Purge / Vent Solenoid P0455

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. 

Basic GM EVAP Overview