Tackling Power Sliding Door Repairs (Toyota Sienta CBA-NCP81G)

Although sliding doors for cars didn’t originate in Japan, they’ve become especially popular in Japanese family cars like minivans, developing a unique culture and practicality.

The widespread adoption of sliding doors in passenger vehicles, especially family-oriented cars, began in the 1980s. This trend was particularly prominent in Japan, where manufacturers started equipping minivans and tall kei cars with standard sliding doors.

The reason sliding doors became so popular in Japan is that they’re easier to open and close in limited parking spaces and narrow roads in urban areas, where conventional hinged doors can make it difficult to get in and out. They also reduce accidents caused by children accidentally opening doors, making them very attractive for family use vehicles.

Subsequent technological innovations added power assist (electric opening/closing mechanisms) to sliding doors, increasing their convenience.

In recent years, I’ve heard from customers that children now recognize power sliding doors as the default for cars, and will patiently wait in front of regular hinged doors or rare manually-operated sliding doors, expecting them to open automatically. When considering the development of automated car doors as technological progress, it makes me wonder whether such ease has truly been beneficial for humans. Nevertheless, power sliding doors have thoroughly penetrated the Japanese family car market and become standard.

Now, when we remove the Sienta’s sliding door trim (interior panel), the following mechanism is revealed:

① is the lock release mechanism (temporarily releases the door lock at the beginning of opening/closing)
② is the power window regulator (door glass lifting/lowering device)
③ is the sliding door control (cable wire winding & feeding device for automatic opening/closing)

Additionally, there’s an easy closer mechanism and a door control module ECU incorporated, with almost everything related to door operation, including the power slide mechanism, concentrated inside the door.

As you can see, a door that houses glass and motors is extremely heavy. It’s no wonder that malfunctions occur when such a heavy component is opened and closed with a primitive mechanism using thin wire cables. But that’s Toyota’s high quality for you. Despite frequent use, it lasted 17 years.

2008 model CBA-NCP81G 1NZ-FE CVT Mileage: 116,000km

While I’m going to perform various maintenance tasks, assembly may be easy but disassembly is not.

First, I remove the door glass. The glass is securely supported by a U-shaped rubber called the glass run, and slides within it. I first pull out this glass run from inside the door panel to create some “play” in the glass. Once the glass can be separated from the window regulator (in this case, we had the additional problem of something separating that shouldn’t normally separate), I remove it at a steep angle from the outside of the vehicle, like solving a puzzle.

There would be a bit more room without the door visor and pillar garnish, but I don’t want to remove the double-sided tape-adhered visor. Furthermore, the glass is heavy and difficult to hold, so I need to carefully find almost the exact angle of removal while ensuring it doesn’t fall or get scratched.

After passing this difficult stage, I can finally work on the internal components and disassemble it until there are almost no parts left inside the door.

The cable wire that caused the malfunction was tangled as you can see.

Next, I preventively address the lock release mechanism, which is a common trouble spot. Normally, genuine parts are only available as the large assembly shown in the photo below:

But since the customer found a motor unit by itself on an online marketplace, I’ll install this instead. This clever approach creates a 25-fold difference in parts cost.

I also fixed the door glass rail that had come loose and was causing problems during raising/lowering, and successfully got everything working normally again.

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