EVAP problems are still among the top 10 codes in the country and tend to be, for us technicians, a pain in the butt when we have to diagnose them — especially with a 0.020” leak. One of the problems that EVAP DTCs present is that the systems are not the same on every vehicle or for that matter not even the same on one OE’s complete vehicle line up. For example, let’s look at Toyota— one EVAP system is not used on all of their vehicles, but rather different variations, sometimes from model to model and year to year. It’s always a good idea to make sure that you look at system description in your service information system before diving into the problem.
It’s increasingly common in the industry to use Identifix or ProDemand to look up a common issue and then change the component that the system identifies as causing the most problems. I am not saying that in many cases they are incorrect, but in a good number of EVAP problems you just may be changing a component that is not going to prevent the MIL from coming back on. EVAP problems have a tendency of coming back and haunting you. Remember that most vehicles from 2001 and newer — when the EVAP leak standard started dropping from 0.040” to 0.020” leak — have leaks that are much harder to find. A good first step is to identify the system type — is it vacuum (the most common that you will find in many cases and used by most OEs), pressure (such as the LDP system used mostly on European vehicles and for a while on Chrysler vehicles) or NVLD (Natural Vacuum Leak Detection) that has been used by almost every OE on newer vehicles that use a 0.020 standard?
Now that we reviewed what we should look for in an EVAP system, the next step is to build your game plan that includes the information from your SI source along with a good smoke machine and/or a CO2 system tester. After retrieving the DTCs then reading the system description, you’re ready to hook up either a smoke machine or a CO2 tester to locate the leak. Smoke machines work well if you know their limitations; if you have a leak in the charcoal canister or in the fuel tank, smoke is going to be very hard to find. Since most smoke is a hydrocarbon base, it’s going to be tough to find a leaking canister or a small hole in a gas tank. The reason that these two problem areas leave you empty handed in most cases when using smoke is the charcoal canister’s job is to trap hydrocarbon vapors, and when using a smoke machine that is exactly what it is doing. I am not to saying that the smoke machine is a useless tool, far from it. In fact, it is very helpful in finding many leaks on a vehicle, and in my shop, we use it all the time. When it comes to EVAP problems, we hook up our Smoke Wizard machine that we have been using for years to check for leaks. We always have CO2 connected to the smoke machine on EVAP issues for two reasons: 1) air pressure is not safe to use since air, fuel and spark will make one hell of a problem; and 2) not every EVAP problem, especially when we have a 0.020 leak, is going to be easy to locate. So if that’s the case, we can easily switch from checking for smoke that works great if there is a broken line or a bad EVAP solenoid, to using our gas analyzer, or better yet using the ATS BullsEye CO2 detector. The CO2 method is just amazing since the CO2 molecule is very small and heavier than air so it drops down. Using CO2 makes the problem of finding a small leak in the system easier.
Our first case study is on a 2010 Ford F-150 that has a capless filler neck. The vehicle came in with P0461 (Fuel Level Sensor Circuit Range/Performance) and P1450 (Unable to Bleed Up Bleed Fuel Tank Vacuum) DTCs. The code descriptions did not exactly provide me with a detailed description of the problem but rather a general check list of just about everything else, almost a process of elimination. When you drill down in the DTC chart and read the possible causes, you find components that may be causing the problem such as solenoids, hoses and the pressure sensor. You may then discover that there is a possible problem in the capless filler neck.
In reading through the service information, Ford recommends the use of their special tool to be used in the capless filler neck and to remove any debris so the filler neck can be tested properly. Ford recommends installing and removing the tool at least five times so any debris around the flap door can be dislodged before using a smoke machine to test. The problem for most shops is that most likely they do not have the special tool. But don’t worry, a capless vehicle comes with a special funnel (Figure 1) that you can use along with duct tape to test the system. So, there is no need to purchase a special tool if you don’t want to, just use the funnel that comes with the vehicle or you can purchase one from a parts store.
Your next step is to place the duct tape on the top of the funnel opening and insert a small hole in the duct tape area so you can insert the hose end of a smoke machine or CO2 tester. On this Ford F-150, the problem was not found from inserting smoke with CO2 from the filler neck down since the neck flaps were the problem causing the DTCs. What we did discover from the test was that the filler neck to the tank was not leaking due to rust or a break that is so common on many vehicles in our area. When we smoked the system from the engine side, we did not come up with any leaks due to the fuel level in the vehicle. We had the owner return when the fuel level was very low so we could re-smoke the system.