Solving your customer's EVAP problems

Sept. 29, 2017
The smaller the leak, the tougher the challenge

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.  

Capless Ford

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.

Figure 1

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.

Smoking the vehicle with a low fuel level, we were able to see a small amount of smoke and a large amount of CO2 escaping from the filler neck. We explained our findings to the F-150 owner and provided him with an estimate that he declined. The F-150 owner thought that it was too much money to spend for a problem that did not affect his driving. What we found was that periodically when the owner fueled his vehicle up, the filler neck flaps would sometimes work as designed and the MIL would go off. My experience on other vehicles with capless filler necks that had a similar issue was better after we installed a new neck. The vehicle owners of the capless system that had the replacement necks no longer experience an illuminated MIL.

Nissan EVAP Issues

This case study is about a good customer of ours who has a 2003 Nissan Altima that came in with the complaint of the MIL illuminated. As usual, we questioned the vehicle owner on when she first noticed the check engine light illuminate — was it after getting fuel, was the gas level low, what was the temperature at the time, etc. We looked at the most obvious, the gas cap, to make sure it was installed properly, followed by a good visual under the hood to see if anything was obvious. Next, we connected our scan tool and found a P0442 EVAP Control System Small Leak Detected. This EVAP system is the basic vacuum system I explained earlier, which uses the engine’s vacuum and a purge valve that is normally closed, not allowing any vacuum or EVAP vapors to pass through it, along with a canister vent valve that is left open until they are both commanded by the PCM. Once commanded by the PCM for system EVAP testing, the purge valve is duty-cycled open to allow a suction while the vent is still open. When the PCM has pulsed the purge valve enough, it first closes the vent followed by closing the purge valve. This action has trapped a vacuum that we can test for decay (vacuum loss) to determine in a set amount of time if the system has a large or small leak.

The problem with this type of system is that a leak can be confused with any pressure change from the vacuum leaking out, to a clog in the system due to insects or debris blocking the vent line or valve. Understanding the system, we thought that this would be really easy to find the problem using our Smoke Wizard along with CO2. As we started to flow smoke with CO2, we noticed that there was in fact a small leak coming from the rear of the vehicle where the charcoal canister, vacuum cut-off valve, vacuum bypass valve, pressure sensor and vent valve are located.

Figure 2

The DTC can be caused by a list of 20 different problems from the gas cap to foreign matter caught in the EVAP canister to a leaking component. In our case the EVAP system’s canister vent valve could no longer provide a complete seal and needed to be replaced. You may be thinking, “Big deal, that’s easy; just change the vent valve.” If you have not worked on one of these Nissan Altima’s, you are sadly mistaken as this system requires that the rear subframe (Figure 2) be dropped to replace the valve properly. I have read that some Nissan techs remove the gas tank instead so they do not encounter problems with the frame rail studs that can break. We have done a few of these and have seen the rust and the potential problem so we spray the studs with penetrating oil and have the owner come back at least two times so that we can respray the studs before performing the subframe removal. Now that the subframe is out of the way, we can easily get into the EVAP area and replace the valve and in this case replace a few vacuum lines as well.

Since the vehicle owner understood the time and labor cost of the job, they took our suggestion and thought it was a good idea to replace the complete EVAP assembly. Our Nissan dealer confirmed that the valve is usually sold as an assembly and that is how their service department performs the repair on these vehicles. I guess if you look at the age of the vehicle and the labor involved to replace the valve, it’s a better bang for the buck to replace all the EVAP components. We all understand that in an older vehicle sometimes you replace one part and then another seems to go not that long after you repaired the vehicle.

Figure 2

Remember that a vehicle owner does not know the difference in codes when the check engine light illuminates; he or she just know the light was on and they paid you to turn it off. It is sometimes difficult to explain to the vehicle owner that the check engine light can illuminated for many different problems. In my shop, we always print out scan tool reports and provide pictures to the owner and save digital copies on our computer. If the owner of this Nissan only wants the vent valve replaced, we would have documented the complete repair with pictures and noted on the invoice that the other components may fail and illuminate the MIL light for possibly the same DTC P0442. If this happened, we would have to charge them the complete amount of labor for the job again. Lucky for us, this customer understood and agreed to perform the complete repair making it unlikely that they would come back with an EVAP leak from that area. We tested the EVAP system for leaks with our Smoke Wizard (Figure 3) to make sure, before we reinstalled the subframe, that the vehicle would pass a 0.020 leak check. Now that we were confident that the vehicle’s EVAP system was repaired, we returned the vehicle to the owner and moved on to the next job.

2006 BMW 320I P0456 small leak
Sometime European EVAP systems put a scare into a technician who is not familiar with these vehicles. Sometimes it’s easier than you think. In the case of the BMW that came into our shop with a small EVAP leak, knowing how to proceed in your diagnostics is a very important step. For instance, on a BMW we have to find out if the system uses an LDP (Leak Detection Pump)/DM TL (Diagnostic Module Tank Leakage) or an NVLD (Natural Vacuum Leak Detection).

Figure 4 Figure 5

Once you find out what system it uses you then can plan your course of attack. In our problem BMW, it uses the DM TL system so we are first going to perform a scan tool test (Figure 4) using the EVAP leak test. Step one is to make sure that the fuel tank is 15 percent to 85 percent filled, followed by making sure the battery voltage is good. In most cases it’s better to place a battery maintainer on the vehicle to prevent the battery from draining down since theses vehicle can suck the battery down quickly and the test can take over 10 minutes to perform.

Figure 6

After you completed the following checks you’re ready to move on to test the system right through the scan tool. The first test performed IDs the large leak test that must pass to perform the small leak test that in this case we know we have. After the large leak, the scan tool will come up with a screen that confirms it failed (Figure 5) the small leak test. I connected the EVAP tool test hose to the canister as per BMW directions and use the BullsEye leak detector to locate the leaking area. What we found really amazed me, since it seemed that CO2 was leaking right out of the wire harness. I confirmed the leak by using the BullsEye foam (Figure 6) that turned yellow. We replaced the part and retested the system using the scan tool small leak test that no longer failed.

While I was researching some service information on another BMW EVAP system I was working on, I found a service bulletin stating that the BMW sensors can possible have a sealing problem that can cause an EVAP leak. Finding and repairing this BMW was not that hard of a job. Just try reading up on the system that you’re working on and know the capabilities of your scan tool, and you’re on your way to a successful EVAP repair.

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