This 2002 Chevrolet Cavalier 2.2 came into the shop with a DTC P0440 Evap Emissions System Fault. The first thing we did was to give a visual inspection of the EVAP system.
We did not see any obvious problems, such as, broken or disconnected hoses, unplugged components (i.e. purge or vent solenoid), broken wires, or loose/missing gas cap.
Many people, when presented with this code, will automatically replace the gas cap. While these caps do need replacing from time to time for maintenance issues, this may not solve the problem. In this case, the gas cap was not the issue.
We then decided to use our diagnostic tool and, using its bi-directional command capability, commanded the purge and vent solenoids on and off. When we did, we heard (and could feel) each one turning on and off as we commanded it. We did this several times to ensure there was not an intermittent problem with sticking in the solenoid.
Next, we connected our smoke machine, which we use to check for EVAP leaks. Again, using the diagnostic tool, we commanded the vent solenoid on (which closes the valve . . . this valve is normally off and thus open, to do the test it must be "On", meaning the vent is closed, so as to allow the system to hold the smoke in), and tested the system with smoke.
The picture below shows the evidence. It is a bit hard to see, so we have drawn an arrow to point to the evidence. What we saw was smoke boiling out of the vent solenoid, even though we were commanding it "On", thus closing the vent. Therefore, with the vent "On" no smoke should have been escaping.
With this evidence, we removed the vent solenoid. What we found is that someone had tie-strapped the diaphragm. More than likely, a previous owner (our customer said they had not done this) knew about the problem and tried to rig it to work. Not a good idea. The solenoid was actually leaking from around its diaphragm, so a new one was in order. A picture of the old one, tie-strap still on is below.
The next picture shows the new vent solenoid in place.
Just FYI, there is a short wiring harness (see below) connected to the vent solenoid. These are notorious for fraying and breaking, due to rear end movement. Like the gas cap above, this was not the cause of this failure. Silver bullet fixes usually end up costing a customer far more money than simply taking it in to a professional to have it properly diagnosed and repaired.
Here is the short wiring harness (I am pointing to it in the picture).
After completing the repair, we cleared the codes and data associated with it. We then ran a EVAP system test with our smoke machine. The test passed. A picture of that is below. You will notice the green lit LED indicating the test completed and passed.
There are many variables when it comes to diagnosing and repairing an EVAP system. A basic understanding of how the EVAP system works on that particular make and model is essential. A visual inspection is always the first place to start.
Don't jump at silver bullet fixes. You may get lucky and it may be your problem and repair your vehicle. Then again, you may spend quite a bit of money chasing several silver bullets and in the end be left with the original problem.
When in doubt, find a professional you can trust and take it to him/her and let them do the proper diagnostics and repairs. It may end up saving you far more money in the long run.
I know the economy has been rough and times are tough. But, throwing parts at a problem can compound that problem quickly.
