Back on the Bench - August - 2019

The Long Way Around: Some Simple Testing on Nissan’s RE0F10A

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CVTs have been around for some time but there’s always been one nagging part that keeps people from working on them: Getting the parts. Sure, the information is available; there are workshops and seminars all across the country but when it comes time to actually work on one about the best you’ve been able to do is replace them. Times are changing and parts are easier to find so let’s jump right in and go to work.

One of the more popular units is the Nissan RE0F10A. There’s a lot of them on the road and they’re easy to work on. Not to mention, parts are available.

One of the most common problems we see are secondary pressure solenoid and secondary pressure sensor codes. The code sets when the computer sees secondary pressure lower than what is being commanded. In order to diagnose this, we must first understand how it works.

The computer controls the secondary circuit pressure by operating the secondary pressure control solenoid, which feeds fluid pressure to the spring side of the secondary control valve (figure 1a). Line pressure passes through the pressure regulator valve (figure 1b), to the line pressure control valve then to the bottom two lands of the secondary control valve (figure 1a). This part of the valve controls the flow to the secondary regulator valve spring side. And the secondary regulator controls the fluid flow from main line pressure to the secondary pulley and the pressure sensor. That’s a lot to take in so just know that it’s often a failed solenoid or worn valves in the valve body. But before we rush into it let get a scan tool on it and look at some data.

First, we’ll take a look at the secondary pressure sensor. If the vehicle is capable of moving you should see some pressure signal at that sensor. If there’s no pressure signal at the sensor then you most likely have a problem with either the sensor or wire harness (figure 2). It’s also possible that you have a computer problem but that’s less likely. What you’re looking for here is an open in the circuit.

However, if we do have a pressure signal on the scan tool then we’ll compare the amperage on the scan tool to the actual amperage in the circuit (figure 3). We do this to make sure there isn’t something wrong with the computer’s ability to operate the solenoid.

Next, install a pressure gauge and monitor line pressure and secondary pressure (figure 4). Low line pressure could be caused by low fluid, the flow control valve (figure 5) or a pressure regulator valve problem (figure 1). If the line pressure is good and secondary pressure is low, this could be caused by the solenoid, valves or a leak in the circuit.

In our case the line pressure was low on the secondary circuit so we pulled the valve body to inspect it. Problems with the pressure regulator or line pressure control valve would have been seen in the line pressure test. This narrows it down to the secondary pressure control, and the secondary pressure regulator in the valve body. It could also be a problem with the secondary pressure solenoid, or leak in the circuit. You’ll want to rule out the valves by making sure they’re free and that they pass a vacuum test.

With the valve body eliminated, our problem is either a solenoid or a leak in the circuit. Testing the solenoid takes some expensive equipment that most people can’t justify unless they are rebuilding solenoids. The only way to test the function of the solenoid without this equipment is to swap it out with another solenoid. Fortunately removing the valve body is easy.

At this point you’ve most likely found the problem and made the repair. However, sometimes it’ll work fine and test right when it’s cold and begin to lose pressure as it warms up. This is fairly common and were having a reliable parts supplier comes in handy. There are a few things to check for this problem: the seals on the pulley apply piston and the sealing ring in the cover (figure 6).

CVTs are just like any other transmission in that they each have common malfunctions and failures. This condition is common, and although we took the long way to cover the diagnosis, you’ll find that this problem usually winds up being a worn valve body or piston seals. These units are easy to work on and straight forward fix. More and more people are working on these units with success. You should too.