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CAR TALK

by Ray Magliozzi | January 23, 2021 at 1:44 a.m.

DEAR CAR TALK: I am Deepak, once of India and the U.S., and now living in Canada, eh.

I often lose air pressure only in the front right wheel. It usually happens when the outside temperature drops or rises all of a sudden. I have a 2015 Toyota RAV4 AWD. And yes, it is silver in case you need to know the color.

Thank you for bringing a pure joy to millions. — Deepak

DEAR READER: Thanks, Deepak. By the way, j-o-y is not how you spell "misery."

The good thing about tires is that there are a limited number of things that can cause them to leak. It's a problem even I can usually solve.

Obviously, if you drive over a screw or nail, or otherwise puncture the tire itself, you'll lose air. But that kind of tire injury usually results in a pretty constant loss of pressure, not an intermittent one.

The second way air can escape is from the bead, which is where the rubber at the inside edge of the tire pushes against the inside of wheel rim. That bead should seal airtight. If the wheel gets bent, for instance, from driving through a pothole the size of Saskatchewan, that can create space between the tire's bead and the rim and allow air to seep out. And it could leak only under certain conditions, like when the tire flexes a particular way over bumps or on turns or when it's parked in a specific position. Or the metal wheel itself can corrode over many years and make it impossible to create a tight seal against the rubber bead. Your car's a little young for that, but since you live in Canada, maybe you've seen more than your share of road salt, eh? So it's possible.

The third way tires tend to leak is from the valve stem. There's a device called a Schrader valve inside that valve stem that lets air go in but not out. And if that's failing, air can escape that way.

So here's what you do, Deepak: Take your RAV4 to a recommended tire shop. They'll fill your tire, take that wheel off the car and put it in a vat of water. It may take a little time, but if there's air coming out, they'll see the air bubbles and figure out where it's coming from.

If they don't see air coming out, it's possible that in order for the leak to occur, the weight of the car has to be on the tire. If it won't leak for them in the water, then I'd have them remove the tire from the wheel, clean up the inside of the rim in case there's rust there, apply plenty of the cement that goes between the bead and the wheel and then remount the tire with a brand-new filler valve.

I'd say that'll give you an 80% chance of solving the problem. If not, take it back, have them remove the tire again and remount it on someone else's car. Good luck.

DEAR CAR TALK: I have a 2016 Toyota RAV4 hybrid. Over the past year, the motorized rear lift gate has not been functioning properly. It would not close when you pushed the button, or it would close a couple of inches and stop. It would take several attempts at button pushing before it would lower, or I would have to close it manually (which is hard to do).

My dealership has provided me good service since I bought the car, so I took it there three times over the past six months. The first time, they said it was working fine (the problem is intermittent). The second time, the mechanic said he lubed the lift pistons, and it was working again. It did, for a day. The third time the mechanic said they checked it with their computer sensor, whatever that means, and "it is working great now." It worked for a day or so. Now it is not opening fully and is even harder to push manually.

I hate taking it back in, because it'll either work perfectly for them or it will malfunction once, they'll do something and declare it fixed when it's not.

Any idea what it is? — Charlotte

DEAR READER: I think you have a problem with the motorized tailgate. How's that for blazing insight? I'm not sure what it is, but I know that Toyota had problems with the computer that controls the power back door.

And yes, Charlotte, there's an actual computer that controls your power back door. What a time to be alive, huh? Toyota even offered to replace the computer (called the PBD ECU or the Multiplex Network Door Computer) for free for customers who had malfunctioning rear doors.

The primary complaint from customers was that they loaded something that was too big for the rear compartment and then closed the rear lift gate. The door closed and stopped when it got to the obstruction, as it's supposed to do, but then it wouldn't function after that.

Your problem sounds a little different, but we've seen another service bulletin that said when a certain trouble code comes up in a scan (that's what your dealer did when he "checked it with their computer"), the solution is also to replace that back door computer.

I would guess the part itself costs about $150, and there's not much labor involved. It's two bolts and a couple of plugs. But if you first complained about this while the car was under warranty, they owe it to you for free.

And even if your warranty had expired before this problem surfaced, it hadn't expired by much. So ask them if they'd show you some goodwill and fix it, since it clearly should last a lot longer than it did.

It's always possible that it could be a bad motorized piston (the motor that actually opens the door, and you have two of them) or the sensor that lets the computer know when an object is in the way. But since we've seen many complaints about the PBD ECU, and we know Toyota has had to replace a bunch of them for free, that's where I'd start.

Plus, those other parts cost a fortune, so we hope the computer fixes it. Good luck.

Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting cartalk.com.

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