EVAP case study: 2005 Mini Cooper

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EVAP case study: 2005 Mini Cooper


How to get started diagnosing real-world problems

Part one in a series

Alex Portillo is the head technician for Car Clinic, an advanced repair shop in Mahopac, N.Y. He has received much of his training from Technicians Service Training and is a pupil of automotive trainer G. “Jerry” Truglia.

In the following case study, we aim to give a good overview of how you can get started diagnosing real-world EVAP problems. In the future, we will cover more advanced EVAP problems.

A 2005 Mini Cooper rolled into the shop with a check engine light. After scanning the codes we saw that what we were dealing with was a small Evaporative Emission Control System (EVAP) leak.

Now, the first thing we do as a matter of protocol is check the fuel cap, delete the code, and send the customer on his way. After all, half the time the customer simply did not tighten his cap or the cap itself has an obvious defect.

Customers do not like paying for a $100 diagnosis in order to find out that all they needed was a $15 part, so we deleted the light and told him to get a cap. So, when he comes back, the cap won’t figure into the diagnosis. When you are doing this, it is also good to take a peek at the fuel filler neck. Is there excessive rust where the cap meets the seal on the cap? Is it a Subaru? These are things that are worth investigating.

After having followed this protocol, the car came back, so now we knew it was time for a serious diagnostic checkup.

So, we got all my “go to” EVAP tools out in preparation for our work. This includes a smoke machine, BMW fuel filler neck adapter (there are a different sizes), smoke machine and CO2 tank. It is good to use CO2 gas instead of shop air as not only a safety precaution, but also so you can find leaks on top of the gas tank or those you cannot see with an emissions analyzer.

Because we were working with a European vehicle, my weapon of choice was the Autologic.

This scan tool has the ability to run tests that the factory scan tool can, and a lot of factory scan tools have an EVAP leak test. This test is useful to run before a diagnosis, because if the vehicle fails it confirms that whatever is setting the check engine light on the vehicle is still present.

After all, do you really care that the vehicle has an EVAP leak? No! You care that the PCM thinks the vehicle has an EVAP leak!

Smoke the car

The Mini failed the test, so we knew it was not an intermittent problem or PCM issue. Now it was time to smoke the car. The Mini, even though it is European, is an LDP system, meaning it uses a leak detection pump on its system. A lot of Chryslers and Mazdas (among others) have this, so we had no reason to be intimidated working on this vehicle.

This is how an LDP system works: it has its own motor (on this vehicle it runs on engine vacuum) that pumps pressure into the system, and sensors measure how long the system can hold pressure. If pressure is lost too quickly, there is a leak somewhere.


This vehicle does not use natural vacuum pressure from temperature changes of the gas and then monitor it for lost vacuum, thereby giving away the fact that outside air is getting in from a leak point. This would be how newer Natural Vacuum Leak Detection (NVLD) systems work. The Mini, for all intents and purposes, is not a complicated system.

On older vehicles, it is wise to start by looking under the hood to find the reverse-thread EVAP test port. Remember to turn the cap off the Schrader valve clockwise, or you might break it!

Sadly, manufacturers have abandoned the test port because it creates another point of leaking, so quite often you will need a filler neck adapter to put in place of the gas cap. This is what we had to do with the Mini.

So, we simply began by smoking the Mini from the filler neck. We placed a plastic crimper (not vice grips, which can create a whole other EVAP leak) on the rubber hose before the EVAP filter, closed the vent solenoid with the Autologic (or you can use a Power Probe), and plastic caps to plug up the hoses leading to the leak detection pump. This allows us to get smoke throughout the whole system without smoke leaving anywhere.

For example, the vent solenoid is open by default so it needs to be closed to keep fumes in. When you close it, be sure you hear a click to confirm the solenoid is operational.

Before we see any smoke, we want to look at the smoke machine’s flow gauge (here a Smoke Wizard model). The flow gauge is important because it confirms for us how big of a leak it has. If the little ball inside the gauge floats over 0.020-inch, then we know we have a present EVAP leak condition.

Most vehicles should have leaks below 0.020-inch on known good EVAP systems.

You might say, “So what, I knew that because the check engine light was on!” Well, this gauge is great for when you cannot see the leak (because it confirms that you’re not crazy and the leak is there somewhere). And then after we conduct a repair, smoking the vehicle again confirms that we do not have any leaks farther down the line.

Remember, EVAP leaks always go down the path of least resistance, so they will leave from the big leak first and then from the smaller leak if there is one.

So, do not let yourself get burned and have a comeback. Be sure to inform your customer that you always fix what you see broken first and if you don’t see anything else after retesting, you stop. This way, if another leak does develop, the customer won’t be calling for your head!

When smoking the Mini we were lucky and immediately found that smoke was pouring out of the EVAP canister. The right rear lift point was missing on this vehicle, so the canister probably became the lift point one day, hence the board of wood on the frame.

The vehicle was fixed by replacing the canister. To protect ourselves against any comebacks, we smoked the system again and made sure the flow gauge showed a much smaller leak (less than 0.010-inch is a safe number) and did another EVAP test with the Autologic.

If the PCM sees no evil, neither do we!   ‚óŹ

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